HPV16-Specific T-Cell Responses and Spontaneous Regression of Anal Intraepithelial Neoplasia

Background: 85% of anal cancers are attributable to persistent human papillomavirus type 16 (HPV16) infection. The anal cancer precursor, high grade anal intraepithelial neoplasia (AIN), is common (prevalence >30%) in MSM. High grade disease frequently regresses spontaneously. We hypothesized that T cell immune responses may contribute to its regression. Methodology: We measured systemic T cell responses to HPV16 oncogenic proteins E6 and E7 (synthesized as overlapping peptides) in a substudy of the Study of the Prevention of ANal Cancer (SPANC). This is a natural history study of anal HPV and AIN in MSM aged ≥35 years, in which anal Papanicolaou smears and high resolution anoscopy (with biopsy of visually abnormal lesions) are performed at five visits over three years. At one visit, peripheral blood was taken for a novel assay for CD4 antigen-specific T cells based on CD25/CD134 co-expression after 44 hours culture, and an intracellular cytokine stain (ICS) assay for interferon-γ (IFNγ) and interleukin-2 (IL2) from CD4 and CD8 antigen-specific T cells. For both assays and each participant, negative and positive (staphylococcal enterotoxin B, cytomegalovirus lysate } CEF peptides) controls were used. A positive response was defined as stimulation index ≥2 and an absolute cell count ≥20 for CD25/CD134 assay (or ≥15 for ICS assay) after subtracting background. Absolute T cell counts were measured with TruCountR tubes. High grade disease was HSIL on cytology and/or AIN2/3 on histology. We tested for associations using Pearson chi2 tests. Results: See table for descriptive results. In cross-sectional analyses, 32.3% of HIV+ men had CD8 T cell responses (IFNγ and/or IL2) to E6 vs. 14.6% of HIV-negative men (p = 0.027). 23.5% of men with high grade disease had IFNγ CD8 T cell responses to E7 vs. 9.6% of men without (p = 0.028). Using longitudinal cytology / histology data from the main study, 26 men had high grade disease at study entry a mean 1 year prior, of which 6 experienced spontaneous regression by the time these assays were performed. Five (83%) of these 6 regressors had CD4 T cell responses to E6 on the CD25/CD134 assay vs. 35% of non-regressors (p = 0.037). ICS responses (CD4 or CD8) did not associate with regression. Conclusions: Systemic HPV16-E6 and E7-specific T cell responses were detected in a substantial proportion of MSM. E7-specific CD8 T cell responses were more likely in those with high grade disease. E6-specific CD4 T cell responses were associated with recent high grade AIN regression.