Transcriptional and functional analyses of neoantigen-specific CD4 T cells during a profound response to anti-PD-L1 in metastatic Merkel cell carcinoma

Background

Merkel cell carcinoma (MCC) often responds to PD-1 pathway blockade, regardless of tumor-viral status (~80% of cases driven by the Merkel cell polyomavirus (MCPyV)). Prior studies have characterized tumor-specific T cell responses to MCPyV, which have typically been CD8, but little is known about the T cell response to UV-induced neoantigens.

Methods

A patient in her mid-50s with virus-negative (VN) MCC developed large liver metastases after a brief initial response to chemotherapy. She received anti-PD-L1 (avelumab) and had a partial response within 4 weeks. Whole exome sequencing (WES) was performed to determine potential neoantigen peptides. Characterization of peripheral blood neoantigen T cell responses was evaluated via interferon-gamma (IFNγ) ELISpot, flow cytometry and single-cell RNA sequencing. Tumor-resident T cells were characterized by multiplexed immunohistochemistry.

Results

WES identified 1027 tumor-specific somatic mutations, similar to the published average of 1121 for VN-MCCs. Peptide prediction with a binding cut-off of ≤100 nM resulted in 77 peptides that were synthesized for T cell assays. Although peptides were predicted based on class I HLAs, we identified circulating CD4 T cells targeting 5 of 77 neoantigens. In contrast, no neoantigen-specific CD8 T cell responses were detected. Neoantigen-specific CD4 T cells were undetectable in blood before anti-PD-L1 therapy but became readily detectible shortly after starting therapy. T cells produced robust IFNγ when stimulated by neoantigen (mutant) peptides but not by the normal (wild-type) peptides. Single cell RNAseq showed neoantigen-reactive T cells expressed the Th1-associated transcription factor (T-bet) and associated cytokines. These CD4 T cells did not significantly exhibit cytotoxicity or non-Th1 markers. Within the pretreatment tumor, resident CD4 T cells were also Th1-skewed and expressed T-bet.

Conclusions

We identified and characterized tumor-specific Th1-skewed CD4 T cells targeting multiple neoantigens in a patient who experienced a profound and durable partial response to anti-PD-L1 therapy. To our knowledge, this is the first report of neoantigen-specific T cell responses in MCC. Although CD4 and CD8 T cells recognizing viral tumor antigens are often detectible in virus-positive MCC, only CD4 T cells recognizing neoantigens were detected in this patient. These findings suggest that CD4 T cells can play an important role in the response to anti-PD-(L)1 therapy.

Development of a Single-Institution Virtual Internal Medicine Subinternship With Near-Peer Teaching in Response to the COVID-19 Pandemic

PROBLEM

In March 2020, medical students at the University of Washington School of Medicine were removed from clinical settings in response to the COVID-19 pandemic. As subinternships are required for graduation and an important way to prepare for internship, a virtual subinternship was created to include practical elements of in-person learning and to address limited teaching faculty from COVID-19 inpatient surges.

APPROACH

A virtual, interactive subinternship was developed with case-based teaching sessions, communication and critical literature evaluation skill building, professional development, and creation of independent learning plans. Near-peer teachers (NPTs) were selected from graduating senior medical students who matched into internal medicine. In addition to teaching topics from the Clerkship Directors of Internal Medicine curriculum, NPTs engaged in course development, recruited teaching faculty, gathered feedback, and facilitated small groups. Participating students completed pre- and postcourse surveys.

OUTCOMES

The 10 students (100%) enrolled in the course who completed both surveys indicated significant improvement in mean scores across 4 domains: evaluating medical literature (3.1/5 to 4.5/5; +1.4, P < .001); developing individual learning plans (3.6/5 to 4.7/5; +1.1, P = .001); perceived ability to efficiently evaluate patients with common internal medicine concerns (3.7/5 to 4.6/5; +0.9, P = .004); and formulating initial diagnostic and therapeutic plans (3.6/5 to 4.6/5; +1.0, P < .001). Themes extracted from open-ended responses included initial skepticism of an online format, the course exceeding expectations, and feeling prepared for internship.

NEXT STEPS

Although a virtual subinternship lacks direct patient care, students reported improvement in all 4 domains studied. Future courses would benefit from greater use of simulation and role-playing scenarios for practical skills. The experience with NPTs was encouraging, aiding in the success of the subinternship. The role of NPTs should be cultivated to fill gaps in content delivery and enhance the development of students as educators.