Over the years cancer treatment mainly involves
three common strategies: chemotherapy, surgical intervention or using
radiotherapy or eradicate cancerous tumour. Immunotherapy has lately emerged as
a fourth strategy to counter cancer. It involves targeting cancer cells through
tumour specific immune cells. These immune cells selectively target the tumour
cells by distinguishing them from normal healthy cells of the body.
The advantage of using T Cells immunotherapy is that
because it utilises antigens for recognistion hence it can target metastatic
cancer cells aswell. Furthermore, as T cells have memory hence it maintains
therapeutic efficacy for many years post immunotherapy.
Adoptive cell therapy (ACT) involves the use of
lymphocytes which are specific for a tumour type. These tumour specific
lymphocytes are obtained from patient blood or from tumour cells and their
expansion and activation is done ex vivo thereby they are infused back into the
patient or polyclonal peripheral T-cells are modified genetically by
incorporating a tumour specific receptor in order to generate tumour specificity
for the immunotherapy (1-3).
1.1 Hisorical background of ACT
The first T lymphocytes function was elucidated in
the 1960s where it was ascertained in experiemental animals models that
allograft rejection was mediated by the T lymphocytes. In those years the
expansion and manipulation of T cells in
culture media was not possible so the T cells could not be used to treat
allograft murine tumours.
In small sized tumors slight inhibition of tumor
growth was observed by the use of syngenic lymphocytes which were highly immunized
against the tumor cells (4, 5). It was suggested in preclinical
studies that the host inhibitory factors have a role to play in this and
chemotherapy or radiation before transfer of cells caused depletion of
lymphocytes so it enhanced the ability of transferred T lymphocytes to treat
tumor cells through immunotherapy (6, 7).
In 1976 Interleukin-2 (IL-2) which is a T cell
growth factor was described for the first time. This provided an opportunity to
grow T lymphocites ex vivo without affecting the effector functions of the
lymphocytes hence paving way for ACT (8). High doses of IL-2 when administered directly in mice
inhibited the tumour growth (9), and subcutaneous lymphomas were
successfuly treated by immune lymphocytes which underwent prior IL-2 expansion
before intravenous injection (10). The
therapeutic potential of these lymphocytes was enhanced by the addition of IL-2
post cell transfer (11). In some patients of metastatic
melanoma administration of IL-2 could effectively cause longterm regression in
tumour mass (12). This gave an impetus for the the
specific T cells and their respective antigens identification for these cancer
immunotherapeutic agents. The main source of lymphocytes which were capable of recognising
tumor in vitro were the ones infiltrating in the stroma of growing,
transplantable tumours. The transfer of these adoptive syngenic tumor
infiltrating lymphocytes which were expanded in IL-2 could regress liver and
lung tumors in murine models (13). Tumor
infiltrating lymphocytes from melanomas showed that these contained specific cells
which had the capability to selectively recognise tumors which were autologous (14). In 1988 it was
demonstrated for the first time that adopted cell therapy by the use of
autologous tumour infiltrating lymphocytes in metastatic melanoma patients
could cause significant regression of cancer (15).
In mature culture cells of Tumour infiltrating lymphocytes (TILs) the
main population of cells is of CD8+
and CD4+ T cells. In cancer patients the propencity of T lymphocytes
to induce regression of tumor gave first insight into cancer immunotherapy in
humans. But, a fundamental issue was that the TILs were almost inexistent in
the blood circulation just after few days of injection and the duration of
action was very short. Improvement in ACT therapy for the treatment of cancer
was first observed in 2002 where it was observed that non-myeloablative
chemotherapy given before TILs injection could cause lymphodepletion which
resulted in increased efficacy of immunotherapy with significant improvement in
cancer regression and in some patients 80 % of the CD8+ of the injected TILs were found
circulating in the blood even after months post administration (16).
1.2 Adoptive Cell Therapy with T-Cells
Adotive cell therapy resulted in
78 % remission in chronic lymphoblastic leukemia patients as observed in
initial clinical trials (17, 18). Although these
are encouraging results in initial clinical finding but the effects of ACT in
solid tumours is not very promising, for instance the reponse rate in
metastatic melanoma patients is only 22 % (19-22). These in vivo
results are the factors which limit the ACT and its overall effectiveness as
immunotherapeutic agent (23). In ex vivo the ACT T-cells
imparts vigorous effector response but in tumour microenvironment or in
lymphatic organs in vivo they rapidly undergo immune suppression. As a result
of a diverse set of immunosupression mechanisms in tumour tissue including the
incorporation of host immune cells causing suppression, production of immunosuppressive
factors inside tumour and due to the activation of negative signalling pathways
which are co-stimulatory (24) the ACT T-cells become non
functional before the eradication of the tumor (25).
1.3 Targeted molecular immunotherapy
deliver immune modulating drugs at a selective tumor or tumor involving lymph
nodes the challenge is to design such a therapeutic modality which is selective
and has minimum systemic non specific
stimulation. To achieve targeted drug accumulation in tumor tissue post
systemic distribution employs a strategy involving drug conjugation with
specific tumor antigen ligand, antibody or other binding moiety. Pro-inflammatory
cytokines are fused with tumor associated antigen specific antibodies and this
facilitates the cytokines delivery at targeted tumour tissue. Cytokines can be
attached with C or N terminals of light or heavy chains of IgG molecules (Figures 1A and 1B) (26). Antigen
binding, Fc receptors interaction and taking part in complement cascade
functions of the antibodies are maintained in these orientations. As an alternate to this cytokines
can also be attached with single chain variable fragment (scFv) or fused with
diabodies to preserve the antigen binding property of the antibody. (Figure 1C–E). Binding of
tumor cells with leukocytes has been proposed as one of the mode of action of
the immunocytokines (27-30). The antibody interacts with
antigen presenting surface of tumor in case of the IL-2 immunocytokines while the
binding of IL-2 to the IL-2 receptor on natural killer cells and T lymphocytes
results in promoting effector function and proliferation in the
microenvironment of the tumor. The efficacy of immunocytokines is dependent on
the antibody-dependent cellular toxicity (ADCC) interaction of the component of
the antibody with the Fc receptor domain (31). Because of increased size and
recycling of the fusion protein in endocytes through the Fc neonatal receptor
the immunocytokines as compared to parent cytokine molecules have a longer half
life in blood (32). The safety of immunocytokines
is increased because they can be injected in much lower doses due to increase
in the blood half life (33).
from cytokine targeting to the microenvironment of the tumor, antibodies which
are tumor targeted have also been utilised to instigate innate immunity based
stimulatory signals to destroy the tumor. CpG DNA which is agonist of TLR9 when
conjugated with antibody which is directed against antigen mucin-1 of tumor
regressed tumor size through promotion of ADCC
and Natural Killer (NK) cells activation in mouse model of pancreatic
cancer (34). In Her2 positive breast cancers
and in non-Hodgkin lymphoma CD20 cells are targeted through CPG-antibody
conjugates (35). EGFR and HER2 overexpressing
tumours have been successfully targeted by
this approach along with other cytotoxic signals involving polycytosine/polyinosine
which is an agonist of TLR3. Aptamers are formulated which are bispecific and bind
with EGF of tumor and agonises CD137 (36). When these aptamers are
administered systemically they resulted in regression of tumor in tumor models
and their toxicity level was lower than anti-CD137 antibodies or CD137-binding
aptamers which are untargeted. Immunomodulators can be targeted to tumors
by the use of natural ligands for the tumor cells which overexpress receptors.
For instance melittin which promotes cystolic delivery, a ternary conjugate of
EGF and polyethylene glycol attached to polyethyleneimine backbone was binded
with polyribocytidylic acid (pIC) to tumor cells overexpressing EGFR
results in inflammation and apoptosis of the tumor tissue (37, 38). References :
1. C. A. Klebanoff, S. A. Rosenberg, N.
P. Restifo, Prospects for gene-engineered T cell immunotherapy for solid
cancers. Nature medicine 22, 26-36 (2016).
2. S. A. Rosenberg,
N. P. Restifo, Adoptive cell transfer as personalized immunotherapy for human
cancer. Science (New York, N.Y.) 348, 62-68 (2015).
3. M. V. Maus et al., Adoptive immunotherapy for
cancer or viruses. Annual review of
immunology 32, 189-225 (2014).
4. E. J. Delorme, P.
Alexander, TREATMENT OF PRIMARY FIBROSARCOMA IN THE RAT WITH IMMUNE
LYMPHOCYTES. Lancet (London, England)
2, 117-120 (1964).
5. A. Fefer,
Immunotherapy and chemotherapy of Moloney sarcoma virus-induced tumors in mice.
Cancer research 29, 2177-2183 (1969).
Fernandez-Cruz, B. A. Woda, J. D. Feldman, Elimination of syngeneic sarcomas in
rats by a subset of T lymphocytes. The
Journal of experimental medicine 152,
7. M. J. Berendt, R.
J. North, T-cell-mediated suppression of anti-tumor immunity. An explanation
for progressive growth of an immunogenic tumor. The Journal of experimental medicine 151, 69-80 (1980).
8. D. A. Morgan, F.
W. Ruscetti, R. Gallo, Selective in vitro growth of T lymphocytes from normal
human bone marrows. Science (New York,
N.Y.) 193, 1007-1008 (1976).
9. S. A. Rosenberg,
J. J. Mule, P. J. Spiess, C. M. Reichert, S. L. Schwarz, Regression of
established pulmonary metastases and subcutaneous tumor mediated by the
systemic administration of high-dose recombinant interleukin 2. The Journal of experimental medicine 161, 1169-1188 (1985).
10. T. J. Eberlein, M.
Rosenstein, S. A. Rosenberg, Regression of a disseminated syngeneic solid tumor
by systemic transfer of lymphoid cells expanded in interleukin 2. The Journal of experimental medicine 156, 385-397 (1982).
11. J. H. Donohue et al., The systemic administration of
purified interleukin 2 enhances the ability of sensitized murine lymphocytes to
cure a disseminated syngeneic lymphoma. Journal
of immunology (Baltimore, Md. : 1950) 132,
12. S. A. Rosenberg et al., Observations on the systemic
administration of autologous lymphokine-activated killer cells and recombinant
interleukin-2 to patients with metastatic cancer. The New England journal of medicine 313, 1485-1492 (1985).
13. S. A. Rosenberg,
P. Spiess, R. Lafreniere, A new approach to the adoptive immunotherapy of
cancer with tumor-infiltrating lymphocytes. Science
(New York, N.Y.) 233, 1318-1321
14. L. M. Muul, P. J.
Spiess, E. P. Director, S. A. Rosenberg, Identification of specific cytolytic
immune responses against autologous tumor in humans bearing malignant melanoma.
Journal of immunology (Baltimore, Md. :
1950) 138, 989-995 (1987).
15. S. A. Rosenberg et al., Use of tumor-infiltrating
lymphocytes and interleukin-2 in the immunotherapy of patients with metastatic
melanoma. A preliminary report. The New
England journal of medicine 319,
16. M. E. Dudley et al., Cancer regression and
autoimmunity in patients after clonal repopulation with antitumor lymphocytes. Science (New York, N.Y.) 298, 850-854 (2002).
17. S. L. Maude et al., Chimeric antigen receptor T
cells for sustained remissions in leukemia. The
New England journal of medicine 371,
18. M. Kalos et al., T cells with chimeric antigen
receptors have potent antitumor effects and can establish memory in patients
with advanced leukemia. Science
translational medicine 3, 95ra73
19. N. P. Restifo, M.
E. Dudley, S. A. Rosenberg, Adoptive immunotherapy for cancer: harnessing the T
cell response. Nature reviews. Immunology
12, 269-281 (2012).
20. S. A. Rosenberg et al., Durable complete responses in
heavily pretreated patients with metastatic melanoma using T-cell transfer
immunotherapy. Clinical cancer research :
an official journal of the American Association for Cancer Research 17, 4550-4557 (2011).
21. C. Yee et al., Adoptive T cell therapy using
antigen-specific CD8+ T cell clones for the treatment of patients with
metastatic melanoma: in vivo persistence, migration, and antitumor effect of
transferred T cells. Proceedings of the
National Academy of Sciences of the United States of America 99, 16168-16173 (2002).
22. R. A. Morgan et al., Cancer regression in patients
after transfer of genetically engineered lymphocytes. Science (New York, N.Y.) 314,
23. C. H. June,
Principles of adoptive T cell cancer therapy. The Journal of clinical investigation 117, 1204-1212 (2007).
24. G. A. Rabinovich,
D. Gabrilovich, E. M. Sotomayor, Immunosuppressive strategies that are mediated
by tumor cells. Annual review of
immunology 25, 267-296 (2007).
25. M. Kalos, C. H.
June, Adoptive T cell transfer for cancer immunotherapy in the era of synthetic
biology. Immunity 39, 49-60 (2013).
26. D. Neri, P. M.
Sondel, Immunocytokines for cancer treatment: past, present and future. Current opinion in immunology 40, 96-102 (2016).
27. M. Naramura, S. D.
Gillies, J. Mendelsohn, R. A. Reisfeld, B. M. Mueller, Mechanisms of cellular
cytotoxicity mediated by a recombinant antibody-IL2 fusion protein against
human melanoma cells. Immunology letters
39, 91-99 (1993).
28. H. Dorai, B. M.
Mueller, R. A. Reisfeld, S. D. Gillies, Aglycosylated chimeric mouse/human IgG1
antibody retains some effector function. Hybridoma
10, 211-217 (1991).
29. J. A. Gubbels et al., Ab-IL2 fusion proteins mediate
NK cell immune synapse formation by polarizing CD25 to the target cell-effector
cell interface. Cancer immunology, immunotherapy
: CII 60, 1789-1800 (2011).
30. I. N. Buhtoiarov et al., Differential internalization of
hu14.18-IL2 immunocytokine by NK and tumor cell: impact on conjugation,
cytotoxicity, and targeting. Journal of
leukocyte biology 89, 625-638
31. P. M. Sondel, S.
D. Gillies, Current and Potential Uses of Immunocytokines as Cancer
Immunotherapy. Antibodies (Basel,
Switzerland) 1, 149-171 (2012).
32. C. Giragossian, T.
Clark, N. Piche-Nicholas, C. J. Bowman, Neonatal Fc receptor and its role in
the absorption, distribution, metabolism and excretion of immunoglobulin
G-based biotherapeutics. Current drug
metabolism 14, 764-790 (2013).
33. A. Tzeng, B. H.
Kwan, C. F. Opel, T. Navaratna, K. D. Wittrup, Antigen specificity can be
irrelevant to immunocytokine efficacy and biodistribution. Proceedings of the National Academy of Sciences of the United States of
America 112, 3320-3325 (2015).
34. J. Schettini et al., Intratumoral delivery of
CpG-conjugated anti-MUC1 antibody enhances NK cell anti-tumor activity. Cancer immunology, immunotherapy : CII 61, 2055-2065 (2012).
35. Z. Li et al., Generation of tumor-targeted
antibody-CpG conjugates. Journal of
immunological methods 389, 45-51
36. B. Schrand et al., Targeting 4-1BB costimulation
to the tumor stroma with bispecific aptamer conjugates enhances the therapeutic
index of tumor immunotherapy. Cancer
immunology research 2, 867-877
37. A. Shir, M. Ogris,
W. Roedl, E. Wagner, A. Levitzki, EGFR-homing dsRNA activates cancer-targeted
immune response and eliminates disseminated EGFR-overexpressing tumors in mice.
Clinical cancer research : an official
journal of the American Association for Cancer Research 17, 1033-1043 (2011).
38. M. Yu, J. Lam, B.
Rada, T. L. Leto, S. J. Levine, Double-stranded RNA induces shedding of the
34-kDa soluble TNFR1 from human airway epithelial cells via
TLR3-TRIF-RIP1-dependent signaling: roles for dual oxidase 2- and
caspase-dependent pathways. Journal of
immunology (Baltimore, Md. : 1950) 186,