Intratumoral B lymphocytes are an integral part of the lung tumor microenvironment. Interrogation of the
antibodies they express may improve our understanding of the host response to
cancer and could be useful in elucidating novel molecular targets. We used two strategies to explore the repertoire of intratumoral B cell
antibodies. First, we cloned VH and VL genes from single intratumoral B lymphocytes isolated from one lung
tumor, expressed the genes as recombinant mAbs, and used the mAbs to identify the cognate
tumor antigens. The Igs derived from intratumoral B cells demonstrated class switching, with a mean VH mutation frequency of 4%. Although there was no evidence for clonal expansion, these data are consistent with
antigen-driven somatic hypermutation. Individual recombinant
antibodies were polyreactive, although one clone demonstrated preferential immunoreactivity with
tropomyosin 4 (TPM4). We found that higher levels of TPM4
antibodies were more common in
cancer patients, but measurement of TPM4 antibody levels was not a sensitive test for detecting
cancer. Second, in an effort to focus our recombinant antibody expression efforts on those B cells that displayed evidence of clonal expansion driven by
antigen stimulation, we performed deep sequencing of the Ig genes of B cells collected from seven different
tumors. Deep sequencing demonstrated somatic hypermutation but no dominant clones. These strategies may be useful for the study of B cell antibody expression, although identification of a dominant clone and unique therapeutic targets may require extensive investigation.