Neoantigen-specific T cells in a novel cutaneous squamous cell carcinoma model

Abstract: More than one million cases of cutaneous squamous cell carcinoma (cSCC) are diagnosed annually
in the US and approximately 4% of patients develop metastases and 2% die of cSCC; thus, a similar number
of people die each year from cSCC as melanoma. Immune checkpoint inhibitors (ICI) are a new class of drugs
that have transformed the therapy of multiple cancer types, but only half of cSCC patients respond to ICI
treatment. ICI target receptors on T cells, such as PD-1, that are expressed after activation and function to turn
off T cell responses. The response of cSCC patients to ICI demonstrates the ability of T cells to constrain
cSCC growth. However, it remains unclear the extent to which CD8 and, in particular, CD4 T cells contribute to
immune-mediated control of cSCC. While the focus of anti-tumor T cell responses has been on MHC class I
neoantigens that elicit cytotoxic CD8 T cell responses, there is growing evidence that MHC class II
neoantigens eliciting CD4 T cell responses are critical in constraining tumor growth and enhancing response to
ICI. Thus, there is a critical need to understand the role of CD8 and CD4 T cells, especially the role of
neoantigen-specific T cells, in controlling cSCC growth. We generated a novel physiologic cSCC
transplantable model on the BALB/c background from a solar simulated light-induced invasive cSCC tumor.
Preliminary data supports that T cells constrain the in vivo tumor growth in the cSCC model and that this model
is sensitive to anti-PD-1 treatment. Using bioinformatic approaches with whole exome and RNA sequencing
data, we have identified immunogenic MHC class I and II neoantigens predicted to elicit a T cell response
based on the binding affinity and presentation of the neoantigen:MHC complex and neoantigen expression.
Using melanoma patient data, our lab has previously demonstrated that these characteristics accurately
predict the ability of a neoantigen to elicit a T cell response. The central hypothesis is that both neoantigen-
specific CD8 and CD4 T cells contribute to immune-mediated control of cSCC growth and response to
treatment with vaccination with immunogenic neoantigens alone or in combination with anti-PD-1. To address
this hypothesis, we will determine the role of CD8 and CD4 T cells in controlling tumor growth, identify MHC
class I and II neoantigens that elicit in vivo T cell responses, and evaluate the expression of functional and
inhibitory neoantigen-specific CD8 and CD4 T cells throughout cSCC tumor growth. Then, we will vaccinate
mice with dendritic cells loaded with irradiated tumor cells or immunogenic MHC class I and/or II neoantigens
and compare the efficacy of these vaccination strategies in inducing CD8 and/or CD4 T cells to prevent cSCC
growth and treat cSCC alone or in combination with anti-PD-1. We will demonstrate the requirement for CD8
and/or CD4 T cells through antibody depletion and adoptive transfer. The impact of this project is to 1) identify
the contributions of neoantigen-specific CD8 and CD4 T cells in control of cSCC growth and 2) advance the
application of personalized neoantigen vaccines to treat cSCC alone or in combination with anti-PD-1.

Grant Number: 5F30CA257622-03
NIH Institute/Center: NIH
Principal Investigator: Anngela Adams