Evaluating the role of CD200 in non-small
cell lung carcinoma immune evasion
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Abstract
Lung cancer is the 3rd most common cancer in the UK, accounting for 13% of all new cancer
cases and is the most common cause of cancer death in the UK, accounting for 21% of all
cancer deaths. Over recent years, the introduction of immunotherapies targeting the PD-1/PDL1
immune checkpoint pathway has revolutionised the treatment of non-small cell lung
carcinoma (NSCLC) patients; as a tumour with a typically highly infiltrated immune reactive
tumour microenvironment (TME) rich in neoantigens, NSCLC tumours represent an ideal
candidate for immunotherapies, as reflected in the durable clinical efficacy seen in some
responder patients. However, most patients treated with PD-1/PD-L1 immunotherapies either
demonstrate an initial response followed by disease progression or, in the case of 47-63% of
patients, demonstrate no response or benefit. Therefore, identification of predictive markers
of immune checkpoint inhibitor (ICI) therapy response or the generation of multi-modality
immunological therapies targeting multiple immune checkpoints could greatly improve the
success of PD-1/PD-L1 ICI therapies in NSCLC. One of the most promising strategies for
overcoming resistance and prolonging therapeutic benefit from ICIs is the use of dual immune
checkpoint blockade. Therefore, the aim of this thesis was to determine whether the immune
checkpoint CD200 may be a relevant immunotherapeutic target in NSCLC patients.
CD200 is a type I transmembrane glycoprotein structurally related to the B7 family of receptors
that signals through its receptor, CD200R, which is expressed on several immune cell
populations including those of myeloid lineage, B cells, NK cells and activated T cells.
Engagement of CD200R results in a negative immunoregulatory signal to maintain immune
homeostasis and prevent over-activation of the immune system. CD200 is also expressed by
several solid and haematological malignancies, with its expression correlating with an
increase in immunosuppressive Treg cells, a decrease in memory T cells, and dysfunction of
cytotoxic effector NK cells. Furthermore, CD200 is a potent regulator and suppressor of
myeloid cell function, suggesting that targeting CD200 signalling may decrease immune
suppression and increase the anti-tumour immune response. As a critical regulator of immune
homeostasis in normal lung, CD200 may also be expressed by tumour cells to evade immune
attack and promote tumour growth.
In this thesis, CD200 expression was first characterised in the normal mouse and human lung
where it was demonstrated to be strongly expressed throughout the distal lung by both type I
and type II alveolar cells. Upon malignant transformation, CD200 expression was
demonstrated on both SCC and adenocarcinoma tumours, although to a greater extent in
adenocarcinoma tumours. We suggest that type II alveolar cells, the predominant cell of origin
v
of adenocarcinoma tumours and some SCC tumours, retain CD200 expression upon
transformation as a method of immune evasion.
Furthermore, using a combined RNA-seq and IHC labelling technique the relationship
between tumour CD200 expression and the absolute and relative frequencies of infiltrating
immune cells was established. In SCC and adenocarcinoma tumours, CD200 expression
positively correlated with the frequencies of immunosuppressive Tregs and in
adenocarcinoma tumours, tumour CD200 expression consistently negatively correlated with
the frequencies of cytotoxic NK cells. In vitro analysis of CD200R+ NK cell activity
demonstrated that CD200+ tumour cells induce NK cell dysfunction as characterised by
decreased degranulation, inhibited cytokine production, altered activating receptor expression
and a decreased capacity to kill tumour cells. Blocking of CD200 with an antibody was
sufficient to restore the NK cell anti-tumour response and increase tumour cell death,
suggesting that blocking CD200 signalling in CD200+ tumours could increase NK cellmediated
tumour cell killing. Furthermore, single-cell analysis and IHC labelling demonstrated
that CD200R is expressed on almost all of the infiltrating immune cell subtypes studied,
suggesting immunoregulatory control of the immune response beyond that which was studied
in this thesis. Taken together, this data suggests a mechanism by which NSCLC tumour cells
express CD200 as a mechanism of immune evasion and that blocking CD200 signalling alone,
or in combination with PD-1 inhibition to synergistically increase immune checkpoint therapy
efficacy, may represent a novel therapeutic target in NSCLC