Notably, the protective effect of non-antigen-specific IgA disappeared in both RAG1-deficient and NSG mice (Fig. 4f, Extended Data Fig. 6d) and tumour-derived TSPAN7 and BDNF antibodies showed decreased anti-tumour effects, consistent with the capacity to transcytose through tumour cells (Extended Data Fig. 6e, f, Supplementary Data 7). This evidence concerns the gene BDNF and neoplasm.