CD33 and neoplasm: This enrichment of Bregs was attributed to infiltration and regulation by CD33+ myeloid-derived suppressor cells (MDSCs) that contributed to an immunosuppressive tumor microenvironment [30,31], the latter exhibiting the most significant frequency of somatic IgH hypermutation compared to other TIL-B subsets, with most clones sharing identical IgH sequences [29], and suggesting a high specificity of Ig against tumor antigens.