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IN THE SPOTLIGHT

JAK Mutations as Escape Mechanisms to Anti–PD-1 Therapy Aurelien Marabelle 1 , 2 , Sandrine Aspeslagh 1 , Sophie Postel-Vinay 1 , 3 , and Jean-Charles Soria 1 , 3

1 Gustave Roussy, Université Paris-Saclay, Département d’Innovation Thérapeutique et d’Essais Précoces (DITEP), Villejuif, France. 2 INSERM U1015, Gustave Roussy, Villejuif, France. 3 INSERM U981, Gustave Roussy, Villejuif, France .

Corresponding Author: Jean-Charles Soria, Institut Gustave Roussy and Uni-versity Paris-Sud, 114 rue Édouard-Vaillant, Villejuif 98105, France. Phone: 33-0-1-42-11-42-96; Fax: 33-0-1-42-11-64-44; E-mail: Jean-Charles.Soria@gustaveroussy.fr

doi: 10.1158/2159-8290.CD-16-1439

©2017 American Association for Cancer Research.

Summary: JAK mutations could be one of the primary escape mechanisms to anti–PD-1/PD-L1 immunotherapy

via impaired IFNγ signaling in cancer cells and could be used to identify patients unlikely to benefi t from these

treatments. Cancer Discov; 7(2); 128–30. ©2017 AACR.

See related article by Shin et al., p. 188 (5).

Immune-targeted therapies blocking the PD-1/PD-L1 path-

way are currently revolutionizing oncology for two main rea-

sons. First, the widths of their spectrum of activity in more than

20 different cancer types demonstrate the validity of targeting

immune cells to treat cancers. Second, as opposed to tumor-

targeted therapies, they generate durable tumor responses and

disease stabilizations which translate into overall survival ben-

efi ts for some patients when compared with standard of care.

This paradigm shift from tumor-targeted to immune-

targeted therapies has been inaugurated in melanoma, fi rst

with anti–CTLA-4 antibodies, then with anti–PD-1/PD-L1

antibodies. These drugs have been designed as antagonistic

antibodies to block T-cell coinhibitory receptors. However,

their precise in vivo mechanism of action remains unclear.

A feature often reported in tumor lesions responding to

these treatments is a high level of CD8 + T-cell infi ltrates.

Therefore, it is believed that anti–CTLA-4 and anti–PD-1/

PD-L1 effi cacy relies on the development of an adaptive

tumor-specifi c CD8 + T-cell response. The corollary assump-

tion is that in order to generate tumor responses, T cells need

to recognize cognate tumor-specifi c epitopes presented by

MHC-I molecules on melanoma cells.

The activation of antitumor CD8 + T cells via MHC-I mol-

ecules is usually followed by T-cell IFNγ release and upregula-

tion of membrane PD-1 receptor. Upon exposure to IFNγ,

cancer cells, like other self-cells, can enter into cell-cycle arrest

and upregulate both MHC-I and PD-L1 to their membrane,

therefore preventing, through the PD-1/PD-L1 interaction,

a T-cell–mediated cell cytotoxicity. Therefore, it is believed

that anti–PD-1/PD-L1 therapy works by blocking this nega-

tive feedback loop and allows for T cell–mediated cancer cell

death ( Fig. 1A ).

This rationale is supported by results showing a correlation

between MHC-I binding neoepitope signatures and survival

in patients with metastatic melanoma or non–small cell lung

cancer treated with anti–CTLA-4 and anti–PD-1, respectively

( 1, 2 ). This rationale is also supported by the correlation

between the level of tumor-infi ltrating CD8 + T cells, the level

of PD-L1 expression in the tumor, and the effi cacy of anti–

PD-1 therapy in metastatic melanoma ( 3 ).

However, the majority of patients with melanoma do not

respond to anti–PD-1 monotherapy, including some patients

with high levels of PD-L1 expression and CD8 + T-cell infi l-

trates in their tumor. Moreover, although tumor responses

upon anti–PD-1 therapy are long lasting, some patients can

eventually relapse from their disease. The mechanisms behind

these primary and secondary refractory diseases to anti–PD-1

therapy remain mostly unknown.

The team of Antoni Ribas and colleagues has recently shown

that an escape mechanism found in secondary refractory dis-

ease can be attributed to mutations of genes involved in the

IFNγ pathway, either via loss-of-function mutations in the

genes encoding for JAK1 and JAK2 (with concurrent deletion

of the wild-type allele) or via truncating mutations of the

MHC-I sub-unit beta-2-microglobulin ( B2M ; ref. 4 ). In this

issue of Cancer Discovery , the same team reports that loss-of-

function JAK mutations can also be found in patients with

primary resistance to anti–PD-1 therapy ( 5 ).

Inactivating JAK1 and JAK2 mutations might in theory

impair the downstream signaling of IFNγ receptors and

therefore the ability of IFNγ to induce a cell-cycle arrest of

tumor cells and to upregulate PD-L1 and MHC-I expression

on their outer membrane ( Fig. 1B ). Shin and colleagues

show here in a melanoma cell line generated from a patient

with primary resistance to anti–PD-1 that a missense muta-

tion of JAK1 associated with an amplifi cation of its gene

locus resulted in a 4:1 mutant:wild-type allele ratio. This

high variant allele frequency seemed to correlate with a loss

of function of JAK signaling because of an inability of these

melanoma cells to upregulate PD-L1 membrane expression

upon IFNγ exposure. Other mutations of JAK1/2 and IFNγreceptors ( IFNGR ) were found in both responders and non-

responders, but these were associated with a nonmutated

allele counterpart which should in theory compensate for

the downstream IFNγ signaling. In their series of melanoma

cell lines, they showed that monoallelic loss-of-function

JAK1 or JAK2 mutations are suffi cient to impair PD-L1

upregulation upon IFNγ exposure when these cancer cell

lines have a loss of the wild-type allele. These JAK1 and JAK2

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mutations with loss of function were also found in other

types of cancers, including one case of mismatch repair–

defi cient (MMRD) colon cancer with primary resistance to

anti–PD-1 therapy.

These results are signifi cant because they suggest that JAK

mutations could be used as a genetic biomarker to identify

patients who might not benefi t from an anti–PD-1/PD-L1

therapy. However, the overall incidence of primary inactivat-

ing JAK1/2 mutations reported here remains low at around

5%: 1/23 patients with melanoma; 2/48 melanoma cell lines;

1/16 MMRD colon cancers. But, as suggested by the authors,

epigenetic silencing of the JAK/STAT pathway could also con-

tribute to anti–PD-1 resistance beyond somatic gene loss of

function. Interestingly, patients bearing tumors with inacti-

vating mutations of JAK1/2 or B2M could benefi t from other

types of immunotherapies, such as bispecifi c T-cell engaging

antibodies or CAR-T cells, which should be active in patients

without tumor MHC-I expression or preexisting antitumor

immunity and especially in the absence of PD-L1 tumor

expression. Moreover, pattern recognition receptor agonists

such as Toll-like receptors and STING agonists could directly

activate proinfl ammatory pathways in a JAK-independent

fashion and could therefore overcome the above-mentioned

immune escape mechanisms ( 6 ).

The link between JAK mutation and resistance to IFNγ-

induced PD-L1 upregulation has been nicely demonstrated

by Shin and colleagues in patients with primary anti–PD-1

refractory disease. However, it is not clear here if these inac-

tivating mutations are indeed associated with an inhibition

of cancer cell proliferation or MHC-I upregulation on tumor

cells upon IFNγ exposure, as demonstrated before in second-

ary refractory tumors ( 4 ).

Also, it is not clear if MHC-I expression is an absolute

requirement for anti–PD-1 effi cacy. Indeed, about 70% of cases

of Hodgkin disease present with B2M-inactivating mutations

and therefore no functional MHC-I expression ( 7 ). However,

these patients show dramatic response rates to anti–PD-1

therapy ( 8 ). One hypothesis could be that CD4 + T cells could

also contribute to the antitumor T-cell response via MHC-II

molecules. Interestingly, a recent report has demonstrated

that MHC-II–positive melanomas are indeed showing good

sensitivity to anti–PD-1/PD-L1 therapy ( 9 ).

Figure 1.   Impact of JAK mutations on IFNγ signaling . A, The binding of IFNγ to the interferon gamma receptor (IFNGR1/IFNGR2) activates downstream signaling via JAK1 and JAK2. Upon phosphorylation, a specifi c transcription profi le will be initiated by a homodimer of the transcription factor STAT1, which will bind to the GAS promoter to induce the expression of IFN-stimulated genes. This transcription profi le will result in cell-cycle arrest and an upregulation of MHC-I molecules and PD-L1 to the cancer cell outer membrane. B, Loss-of-function mutations of JAK1 or JAK2 can impair IFNγ downstream signaling and therefore allow for cancer cell proliferation, T-cell ignorance by lack of MHC-I upregulation, and ineffi cacy of anti–PD-1/PD–L1 therapy due to absence of PD-L1 expression.

A

B

CD8+ T-cell

recognition

T-cell ignorance

JAK1 JAK2

Cancer cell

proliferation

GAS

Impact of

PD-1/PD-L1

blockade

Inefficacy of

PD-1/PD-L1

blockade

JAK1 JAK2

β2M

β2M

MHC-I

Cancer cell

MHC-I PD-L1Nucleus

PD-L1

IFNγ

IFNγ

STAT1 STAT1

GAS

Cell-cycle

arrest

IFNGR1 IFNGR2

IFNGR1 IFNGR2

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The absence of infl ammation in melanoma tumors does

not seem to be related to an absence of immunogenic epitopes

( 10 ). Therefore, beyond MHC molecule expression and IFNγ

signaling, other factors contribute to the overall immuno-

genicity of cancer cells and sensitivity to immune checkpoint–

targeted therapies. The ongoing clinical trials testing numer-

ous anti–PD-1/PD-L1 combinations shall hopefully identify

synergistic combinations which will circumvent the predomi-

nant escape mechanisms to single immune checkpoint block-

ade therapy.

Disclosure of Potential Confl icts of Interest A. Marabelle is a consultant/advisory board member for AstraZeneca,

BMS, Merck, Merck Serono, Pfi zer, and Roche/Genentech. J.-C. Soria is

a consultant/advisory board member for AstraZeneca, BMS, Merck,

Pfi zer/Merck Serono, and Roche. No potential confl icts of interest

were disclosed by the other authors.

Grant Support This work has benefi ted from the support of the grant SIRIC

SOCRATE from the Institut National du Cancer ( INCa ).

Published online February 6, 2017.

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PD-1 Therapy− Mutations as Escape Mechanisms to AntiJAK

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