As understanding of the immune system has progressed its use
as a therapeutic for various cancers has also moved forward. This hand in glove
approach has allowed one to go from observation to utilization to modification
and then cycle again. The area of tumor infiltrating lymphocytes and their
application in the area of adoptive cell transfer has been a topic of interest
for almost three decades. The presence of T cells around tumors is a common
occurrence. For example in malignant melanoma there is often such a
proliferation seen upon biopsy.
The question then is; if the immune system acts
accordingly then why does it not follow through and destroy the tumor? We now
understand some of the basics of this process and one suspects a great deal
more will be learned. However the proliferation of the T cells, called Tumor
Infiltrating Lymphocytes, TILs, led early investigators to try and utilize them
as a therapeutic. This was done by ex vivo acceleration and proliferation of
the cells and implanting them back in the patient. This is adoptive cell
transfer. This we shall focus on in this brief note.
Rosenberg and his Lab have for nearly 40 years been
investigating this area. In a 1985 NEJM paper he wrote about his work with autologous
lymphokine-activated killer (LAK) cells:
The administration of LAK cells in conjunction with
interleukin-2 as reported in this paper represents a possible new approach to
the treatment of cancer, with potential applicability to a wide variety of
tumors. A major advantage of this approach is its broad antitumor specificity.
It should be emphasized, however, that this study involved a limited number of
patients and that the frequency and duration of the clinical responses have yet
to be determined.
The practicality and safety of administering this therapy
to large numbers of patients also remain to be fully defined. The similarity of
our initial experience in patients to our prior experience in mice, however,
offers hope that this therapy can be made effective against human cancer.
As noted, this examination of TILs and their function has
been examine for decades. For example, in 1991 Jicha et al (in Rosenberg's Lab)
had noted:
Interleukin 7 (IL:7) is a 25-kD cytokine that was
initially described as a pre-B cell growth factor. This cytokine has also been
shown to have T cell proliferative and differentiation effects. In this report,
we demonstrate that antitumor cytotoxic T lymphocytes (CTL) generated by
secondary in vitro sensitization of draining lymph node cells in IL7 are
effective in treating 3-day syngeneic methylcholanthrene (MCA) sarcoma
pulmonary metastases in mice.
In vivo titrations comparing IL7 to Ib2 antitumor CTL
show that they have equivalent potency in adoptive immunotherapy. IL+-7
antitumor CTL generated against MCA sarcomas of weak immunogeneity are also
tumor specific in their in vivo efficacy. This study represents the first
successful use of a cytokine other than IL-2 for the generation of cells with
in vivo efficacy in cellular adoptive transfer.
Earlier Belldegrun et al (also from Rosenberg's Lab) noted:
The identification, isolation, and adoptive transfer of
selected subsets of immune cells with specific antitumor reactivity into tumor
bearing patients to mediate cancer regression in vivo is a prime goal of tumor
immunology. Currently, however, there are no available techniques for
generating such lymphoid cells with reactivity against specific tumor antigens
in the human.
Recent experiments have demonstrated that the adoptive
transfer of lymphokine-activated killer cells plus IL-2 can mediate tumor
regression in a variety of animal models and human tumors as well. This
approach, however, requires the transfer of large numbers of sensitized fresh
lymphocytes, i.e., more than 1011 immune cells, into tumor bearing
humans, along with the systemic administration of relatively high doses of
RIL-2 (100,000 units/kg body weight i.e. every 8 h).
Many human tumors are infiltrated with chronic
inflammatory cells, including lymphocytes. We have recently identified a
population of lymphoid cells infiltrating murine tumors that could be expanded
in vitro in IL-2 and, when adoptively transferred, were capable of totally
eliminating 3-day established pulmonary metastases. When compared to LAK cells,
these TIL cells were at least 50 times more potent in mediating the therapy of
established micrometastases. The simultaneous administration of IL-2 enhanced
the in vivo therapeutic effective ness of the adoptive transfer of TIL,
although high doses of TIL alone were also effective. The greater therapeutic
efficacy of TIL compared to LAK cells in the treatment of established metastases
in mice raises the possibility that TIL isolated from human tumors and expanded
in vitro in IL-2 may similarly be effective for the treatment of human cancer.
Now in our current understanding these have again attracted
attention as Horton and Gajewski (2018) note:
Tumours from multiple cancer types can be infiltrated by
CD8+ T cells (TILs). TILs are thought to be suppressed by multiple immune
inhibitory molecules in the tumour microenvironment, and this suppression has
been associated with tumour progression.
Therefore, despite tumour infiltration, almost all
tumours containing TILs will progress if not treated. While several immune inhibitory
mechanisms have been identified, immune inhibitory receptors expressed on
activated T cells, like CTLA-4 and PD-1, have received the most attention over
recent years owing to the immense clinical success of PD-1 and CTLA-4 neutralizing
antibodies. The engagement of inhibitory receptors expressed by TILs is thought
to render TILs dysfunctional.
However, evidence from both human tumour samples and
mouse models has suggested that, despite inhibitory receptor expression, TILs
are not functionally inert and actually retain the ability to proliferate,
produce IFN-g and show ex vivo cytotoxicity.
These observations raise the question of why activated
TILs are not able to spontaneously control progressing tumours, and how tumours
that contain TILs might sometimes be resistant to immunotherapies such as
checkpoint blockade. Current immunotherapies can induce durable tumour
regression; however, they benefit a minority of patients: finding new
strategies to increase the response rate to immunotherapies is of great
interest to both researchers and clinicians.
There are many dimensions available for employing the immune
system. Many current foci relate to the T cell elements of the adaptive system.
There are also a multiplicity relating to the innate system including the NK or
natural killer cells. The overall approach requires an understanding of two
things: (i) what makes a tumor cell different and how does it tend to protect
itself, (ii) how do immune systems identify and attack aberrant cells. On the
one hand we look at the malignant cell and how it expresses itself, which we
know is arguably an ever changing process. The second element is how can we use
and manipulate the bodies basic immune system, and here it should be both
adaptive and innate.
There are a multiplicity of ways in which the immune system
may attack cancer cells. We summarize this in the figure below. We have
discussed checkpoint issues and CAR T cells previously and herein we focus on
TIL and ACT mechanisms. All of these mechanisms shown below are somewhat
variants of each other as we shall discuss. TIL/ACT mechanisms are the oldest
in concept and are in many ways a brute force method of attacking the cancer
cells in larger volume than they would have been in vivo.
We will then focus on the interrelationship between the
cancer cell and the immune cell. For each we ask how they are identified, how
they act, and how they may protect themselves. We summarize that below. The
battle is between an immune cell and a cancer cell. The cancer cell can be
identified but it can also protect itself. The self-protection is inherently
part of its ancestry as a descendent of the individuals own cell line. It is a
protection against auto-immune diseases. In contrast the immune cell can detect
cells that do not belong, and as such can then emit attack mechanisms that
destroy the unwanted invader. Immunotherapy is thus a balance between survival
and destruction.
We briefly look at a comparison of some of the techniques. From
Yee we have the following diagram (as modified):
Yee then notes on the above:
Adoptive Cell Therapy is represented by three general
approaches:
1) Enrichment and expansion of tumor-infiltrating
lymphocytes (TIL) from a disaggregated tumor biopsy sample
2) Genetic transfer of T Cell Receptor (TCR) recognizing
tumor antigen-derived peptide-MHC target or Chimeric Antibody Receptor (CAR)
recognizing surface tumor protein
3) Enrichment of endogenous antigen-specific T cells from
peripheral blood mononuclear cells by in vitro stimulation followed by cell
selection or cloning. PBMCs are a source of both antigen-presenting cells and T
cells.
Following enrichment, the population of tumor-reactive T
cells undergoes rapid expansion of 1000-5000 fold achieving 10 - 100 billion
cells for adoptive transfer. Patients often receive a lymphodepleting
conditioning regimen pre-infusion followed by exogenous IL-2. In the case of
adoptive TIL therapy, patients receive high-dose near ablative or fully
ablative conditioning pre-infusion and a course of high-dose IL-2 post-infusion.
… ‘young’ TIL are generated using a shortened pre-expansion culture phase prior
to rapid cell expansion, enabling production of an infusible T cell product
within 5-7 weeks from time of tumor collection.
Here Yee included a multiplicity of techniques. Namely Yee
sweeps any method extracting, modifying, and re-implanting T cells as ACT. We
examine these somewhat and leave them as all separate.
One must recall that T cells are not alone in this fight
against cancer cells. The innate immune system has a powerful set of tools
which are used as an immediate attack mechanism and if properly triggered may
be of adjuvant usage. We have examined the innate system and its various
methods elsewhere. Two strong elements there include the natural killer cells,
NK, and the complement chain. Complement has yet to receive a great deal of
attention as regards to cancer immunotherapy. Looking at Macor and Tedesco we
note:
The contribution of the complement system to the control
of tumour growth has been neglected for a long time as the major emphasis has
been put mainly on cell-mediated immune response against cancer. With the
introduction of monoclonal antibodies in cancer immunotherapy complement has
come into play with a great potential as effector system. Complement has a
number of advantages over other effector systems in that it is made of
molecules that can easily penetrate the tumour tissue and a large majority, if not
all, of the components of this system can be supplied locally by many cells at
tissue site.
Further advances are being made to increase the
anti-tumour efficiency of the complements system using C-fixing antibodies that
are modified in the Fc portion to be more active in complement activation.
Another strategy currently investigated is essentially based on the use of a
combination of two antibodies directed against different molecules or different
epitopes of the same molecule expressed on the cell surface in order to
increase the number of the binding sites for the antibodies on the tumor cells
and the chance for them to activate complement more efficiently.
One of the problems to solve in exploiting complement as
an effector system in cancer immunotherapy is to neutralize the inhibitory
effect of complement regulatory proteins which are often over-expressed on
tumour cells and represent a mechanism of evasion of these cells from
complement attack. This situation can be overcome using neutralizing antibodies
to target onto tumour cells together with the specific antibodies directed
against tumor specific antigens. This is an area of active investigation and
the initial data that start to be available from animal models seem to be
promising.
Thus we believe that a great deal can be garnered by not
only focusing on the adaptive elements but also the innate.
ACT can be interpreted in a broad manner. We now examine
several areas of collateral interest. They are summarized in the following
graphic where we have presented 4 of the eight described above.
Cancer cells are derivative of the body's own cells and as
such reflect an ability to stop the immune system from destroying them. These
surface markers called checkpoints can tell an attacking immune cell not to do
so because this cell is part of the whole, even is expressing clear signs of
aberrancy. The creation of monoclonal antibodies, Mabs, have yielded tools that
work on may cancers and allow for the attack which otherwise would have been
halted.
As Liu et al have noted:
Targeted therapies for cancer with small molecules and
monoclonal antibodies (MoAb) have led to significant improvement in the
long-term survival of multiple malignancies. The discovery of programmed death-
1 (PD-1) and the ligand 1 (PD-L1) has opened the door to the modern era of
cancer immunotherapy. It is well known now that many tumor cells are able to
upregulate the expression of PD-L1 which leads to anergy of cytotoxic T cells
upon PD-1 binding to the ligand. Blocking the PD-1 pathway using monoclonal
antibodies against PD-1 or PDL1 can therefore revamp the immune response
against tumor cells.
The development of MoAbs against PD-1 and PD-L1 has led
to the fast and fundamental paradigm shift in cancer therapy. The anti-PD drugs
are the new form of tumor-site immune modulation therapy through resetting
immune reservoir in the tumor microenvironment. This is fundamentally different
from the conventional chemotherapy and radiation that mainly target cancer
cells themselves.
PD-L1 expression on the tumor cells and immune cells have
become biomarkers that can assist clinical decisions in the choice of treatment
strategies. Biomarker assays for PD-L1 are playing bigger roles and are being
routinely done nowadays. However, PD-L1 assays can be highly variable, which
makes it a clinical challenge to employ the results. In this review, we
summarized latest clinical development of PD antibodies and
immunohistochemistry (IHC) assays for PD-L1 biomarker expression in clinical
practice.
CIK or cytokine induced killer cells, have seen use in multiple
areas. I have reported on their use in the case of MDS, myelodysplastic syndrome,
patients resulting is what the attending physicians have labelled as a cure. As
Jiang et al have noted:
The number of immune cells, especially dendritic cells
and cytotoxic tumor infiltrating lymphocytes (TIL), particularly Th1 cells, CD8
T cells, and NK cells is associated with increased survival of cancer patients.
Such antitumor cellular immune responses can be greatly enhanced by adoptive
transfer of activated type 1 lymphocytes. Recently, adoptive cell therapy based
on infusion of ex vivo expanded TILs has achieved substantial clinical success.
Cytokine-induced killer (CIK) cells are a heterogeneous
population of effector CD8 T cells with diverse TCR specificities, possessing
non-MHC-restricted cytolytic activities against tumor cells.
Preclinical studies of CIK cells in murine tumor models
demonstrate significant antitumor effects against a number of hematopoietic and
solid tumors. Clinical studies have confirmed benefit and safety of CIK
cell-based therapy for patients with comparable malignancies. Enhancing the
potency and specificity of CIK therapy via immunological and genetic
engineering approaches and identifying robust biomarkers of response will significantly
improve this therapy. The presence of cytotoxic tumor infiltrating lymphocytes (TIL)
within tumor is associated with increased survival of cancer patients. Both
antitumor adaptive and innate cellular immunity are important for resistance of
tumor growth and eventual elimination of cancer.
Theoretically, antitumor cellular immune responses can be
greatly enhanced by adoptive transfer of lymphocytes, a term encompassing a
strategy in which autologous T or NK cells are acquired from a cancer patient
and then activated and expanded ex vivo prior to reinfusion.
Adoptive cell therapy of cancer, first demonstrated in
mice more than 50 year ago, has gained momentum in recent years due to
impressive clinical experiences with melanoma patients.
This approach is based on ex vivo expansion of large
numbers of TILs and selection of tumor-specific T cell lines. The major
effectors of TIL cells are phenotypically CD3+CD8+ T cells and their anti-tumor
functions are MHC restricted [5]. In contrast to tumor antigen-specific immunotherapy,
there is potential utility of non-antigen specific cell-based therapy. Many
patients with cancer are ineligible for TIL-based therapy because their TILs do
not expand sufficiently or because their tumors have lost expression of
antigens or MHC molecules or have extremely low numbers of TILs.
Cytokine-induced killer (CIK) cells are a heterogeneous
population of effector CD8 T cells with diverse TCR specificities, possessing non-MHC-restricted
cytolytic activities against tumor cells. Therefore, CIK cells can lyse tumor
cells in a non- MHC-restricted manner and can serve as an alternative cellular
immunotherapy.
The CIK approach is to some degree more akin to ACT but that
it tries to use a multiplicity of immune cells. We believe that using CIKs with
perhaps better targeting and checkpoint inhibitors may have significant
advantages in many malignancies.
ACT can be viewed in broad terms. I believe it is fair to
say that the Rosenberg approach is the classic one of removing TILs and then multiply
them and strengthen them ex vivo and then place them back in the patient,
without any added modifications. CAR-T cell therapy looks at the cancer cell
itself and seeks a unique surface marker, such as CD19, and then designs and
builds a T cell to attack just that marker. As Ott et al note:
Adoptive T cell therapy, CAR-T cell therapy Adoptively
transferred T cells generated from tumor TILs, T cells bearing engineered,
tumor specific T cell receptors, and chimeric antigen receptor (CAR) T cells
all have shown remarkable anti-tumor activity in select solid and hematological
malignancies. CAR T cells and T cells with engineered tumor specific TCRs may
have the ability to induce an inflamed tumor microenvironment and therefore to
be promising partnering strategies with PD-1/PD-L1 blockade.
CAR-T are effective and clearly more than a passing fad. Yet
they are costly to prepare and may miss the critical cancer cells. ACT is a
broad brush approach and hopes that the mix of cells may effectively hit the
target. However the problem is always the stem cell or cell of origin problem.
This is a substantial issue to be faced.
Natural Killer cells are considered part of the innate
immune system. This classification seems to be based upon their sense of
immediacy in responding and the simplicity of their response mechanism. However
NK cells are very powerful tools in attacking malignancies as well.
As Pahl and Cerwenka have recently noted:
Natural Killer (NK) cells are classically considered
innate immune effector cells involved in the first line of defense against
infected and malignant cells. More recently, NK cells have emerged to acquire
properties of adaptive immunity in response to certain viral infections such as
expansion of specific NK cell subsets and long-lasting virus-specific responses
to secondary challenges.
NK cells distinguish healthy cells from abnormal cells by
measuring the net input of activating and inhibitory signals perceived from
target cells through NK cell surface receptors. Acquisition of activating
ligands in combination with reduced expression of MHC class I molecules on
virus-infected and cancer cells activates NK cell cytotoxicity and release of
immunostimulatory cytokines like IFN-.
In the cancer microenvironment however, NK cells become functionally
impaired by inhibitory factors produced by immunosuppressive immune cells and
cancer cells. Here we review recent progress on the role of NK cells in cancer
immunity. We describe regulatory factors of the tumor microenvironment on NK
cell function which determine cancer cell destruction or escape from immune
recognition. Finally, recent strategies that focus on exploiting NK cell
anti-cancer responses for immunotherapeutic approaches are outlined.
One of the concerns regarding immunotherapy is that the
panoply of options may at times be shadowed by a single strand of success and
thus leaving behind a set of tools of great power. The authors continue in
their discussion focusing on the use of NK cells as the entity in adoptive
transfer:
Adoptive transfer of NK cells: To potentiate NK cell
activity, the application of IL-2 in patients has remained challenging because
high doses of IL-2 can result in serious adverse effects and expand regulatory
T cells.
As an alternative, NK cells can be (re-)activated ex vivo
and used for adoptive cell transfer therapy.
In the case of T cells, adoptive transfer using
autologous tumor-reactive T cells (e.g. anti-MART-1) and chimeric antigen
receptor (CAR) T cells (e.g. anti-CD19-CD3+-CD28) achieved significant clinical
responses in some patients with advanced melanoma or B cell malignancies. These
T cells, however, fail to control epitope-negative variants and have the
potential for long-time adverse effects on epitope-positive non-malignant
cells.
Similar to CAR T cells, genetically-engineered CAR NK
cells are currently explored to more specifically direct NK cell cytotoxicity
toward cancer cells. Analogous to therapeutic antibodies, this approach enables
the killing of cancer cells which are otherwise poorly susceptible to NK cell
recognition in addition to ‘natural’ cytotoxicity against epitope-negative
cells.
Adoptive transfer of ex vivo cytokine-activated
autologous or haploidentical NK cells resulted in favorable responses in a
subset of pediatric and adult patients with hematological malignancies without
causing graft-versus-host disease in the recipients.
This discussion expands the set of calls used in an adoptive
transfer mode. Perhaps there can be alternative beyond these as well. My
thoughts would include the complement system and its ability to isolate and
neutralize aberrant intruders.
As much as I find the term "precision medicine"
inaccurate, for we really mean accuracy not precision but I suspect this is a
politically chosen term, the above approaches represent a collection of tools
we now have at our command in treating cancers. In addition we also have
pathway modifies such as kinase inhibitors whose use in such cancers as CML
truly opened the door to treatment based upon detailed knowledge. One suspects
that ultimately cancer treatment will be an integrated usage of all of these
therapeutic techniques and not just one at a time. If we have learned anything
from the treatment of Hodgkins Lymphoma it is that single threaded treatments
are rarely effective and that an integrated approach is essential.
We can now make some overall comparisons as shown below:
1.
Abbas et al, Cellular and
Molecular Immunology, Elsevier (New York) 2018
2.
Belldegrun et al,
Interleukin 2 Expanded Tumor-infiltrating Lymphocytes in Human Renal Cell
Cancer: Isolation, Characterization, and Antitumor Activity, Cancer Research
48, 206-214, January 1. 1988
3.
Cheever et al,
Antigen-Driven Long Term-Cultured T Cells Proliferate In Vivo, Distribute
Widely, Mediate Specific Tumor Therapy, And Persist Long-Term As Functional
Memory T Cells, J. Exp. Med, Volume 163 May 1986 1100-1112
4.
Cynamon, Active
Immunotherapy and Adoptive Cell Transfer as an Effective Cancer Treatment, The
Science Journal of the Lander College of Arts and Sciences, Volume 9 Number 1
Fall 2015
5.
Dudley et al, Adoptive Cell
Therapy for Patients With Metastatic Melanoma: Evaluation of Intensive
Myeloablative Chemoradiation Preparative Regimens, Journal Of Clinical Oncology,
Volume 26 , Number 32, November 10 2008
6.
Eichhoff, Signaling
Pathways In Melanoma, A Dissertation Submitted To Eth Zurich For The Degree Of
Doctor Of Sciences, 2010
7.
Horton and Gajewski, Back
from the dead: TIL apoptosis in cancer immune evasion, British Journal of
Cancer (2018) 118, 309–311
8. Huehls et al, Bispecific T cell engagers for cancer
immunotherapy, Immunol Cell Biol. 2015 March ; 93(3): 290–296
9.
Jiang et al,
Cytokine-induced killer cells promote antitumor immunity, Journal of
Translational Medicine 2013, 11:83
10.
Jicha et al, Interleukin 7
Generates Antitumor Cytotoxic T lymphocytes against Murine Sarcomas with
Efficacy in Cellular Adoptive Immunotherapy, The Journal of Experimental
Medicine, 9 Volume 174, December 1991, 1511-1515
11.
June, Principles of
Adoptive Cell Cancer Therapy, The Journal of Clinical Investigation, Volume 117 Number 5 May 2007
12.
Koury et al,
Immunotherapies: Exploiting the Immune System for Cancer Treatment, Journal of
Immunology Research, Volume 2018, Article ID 9585614
13.
Lesterhuis et al, Cancer
immunotherapy – revisited, Nature Reviews, Drug Discovery, August 2011.
14.
Liu et al, Recent
development in clinical applications of PD-1 and PD-L1 antibodies for cancer
immunotherapy, Journal of Hematology & Oncology (2017) 10:174
15.
Macor and Tedesco, Complement
as effector system in cancer immunotherapy, Immunology Letters 111 (2007) 6–13
16. McGarty, Cancer Immunotherapy: A Systems Approach, https://www.researchgate.net/publication/314090163_Cancer_Immunotherapy_A_Systems_Approach
17.
Mehta and Rezvani, Chimeric
Antigen Receptor expressing Natural Killer Cells for the immunotherapy of
Cancer, Frontiers in Immunology, www.frontiersin.org, February 2018,| Volume 9, Article 283
18.
Norelli et al, Clinical
pharmacology of CAR-T cells: Linking cellular pharmacodynamics to
pharmacokinetics and antitumor effects, Biochimica et Biophysica Acta 1865
(2016) 90–100
19.
Ott et al, Combination
immunotherapy: a road map, Journal for ImmunoTherapy of Cancer (2017) 5:16
20.
Pahl and Cerwenka, Tricking
the balance: NK cells in anti-cancer immunity, Immunobiology, 2015
21.
Rosenberg and Restifo,
Adoptive cell transfer as personalized immunotherapy for human cancer, Science,
3 April 2015 • Vol 348 Issue 6230
22.
Rosenberg et al,
Observations On The Systemic Administration Of Autologous Lymphokine-Activated
Killer Cells And Recombinant Interleukin-2 To Patients With Metastatic Cancer,
NEJM Dec 1985
23.
Rosenberg, The Transformed
Cell: Unlocking the Mysteries of Cancer, 1992, Putnsam (New York) 1992.
24.
Rosenberg, Gene Therapy for
Cancer, JAMA November 4, 1992, Vol 268, No. 17
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cell engager (BiTE®) antibody constructs can mediate bystander tumor cell
killing, PLOS ONE, https://doi.org/10.1371/journal.pone.0183390
, August 24, 2017
26.
Schoof et al, Activation of
Human Tumor-infiltrating Lymphocytes by Monoclonal Antibodies Directed to the
CD3 Complex, Cancer Research 50. pp 138-141, February 15. 1990
27.
Tokuyasu and Huang, A
primer on recent developments in cancer immunotherapy, with a focus on
neoantigen vaccines, J Cancer Metastasis Treat 2018;4:2
28.
Wang et al, Current
advances in T-cell-based cancer immunotherapy, Immunotherapy (2014) 6(12),
1265–1278
29.
Yee, Adoptive T Cell
Therapy for Cancer: Boutique Therapy or Treatment Modality?, Clin Cancer Res
Published OnlineFirst August 6, 2013.
30.
Zhou et al, A kinetic
investigation of interacting, stimulated T cells identifies conditions for
rapid functional enhancement, minimal phenotype differentiation, and improved
adoptive cell transfer tumor eradication, PLOS ONE |
https://doi.org/10.1371/journal.pone.0191634 January 23, 2018
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