Purpose: To determine if serologic recognition of p53 mutations at the protein level depends upon the ability of mutant p53 to express new peptide epitopes that bind to human leukocyte antigen (HLA) class II molecules, we used anti-p53 antibody production as a marker for HLA class II–restricted T-cell involvement in head and neck cancer.

Experimental Design: An anti-p53 antibody response was correlated with specific p53 mutations and the patients' HLA class II alleles and haplotypes. HLA binding studies and in vitro stimulation (IVS) of peripheral blood mononuclear cells were done using a mutant versus wild-type HLA-DQ7-binding p53 peptide.

Results: Certain HLA-DQ and HLA-DR alleles were frequently present in p53 seropositive patients who produced serum anti-p53 antibodies. Selected mutated p53 peptides fit published allele-specific HLA class II binding motifs for the HLA-DQ7 or HLA-DR1 molecules. Moreover, a mutant p53 peptide bound with a 10-fold greater affinity than the wild-type p53 peptide to HLA-DQ7 molecules. IVS of CD4⁺ T cells from seven healthy HLA-DQ7⁺ donors using this mutant p53 peptide (p53_220C) was associated with a partial T helper type 2 phenotype compared with IVS using the wild-type p53_210-223 peptide.

Conclusions: Our results support the hypothesis that mutated p53 neoantigens can bind to specific HLA class II molecules, leading to a break in tolerance. This may lead to skewing of the CD4⁺ T lymphocyte response toward a tumor-permissive T helper type 2 profile in head and neck cancer patients, as manifested by seropositivity for p53.