We hypothesized that the respiratory symptoms observed in patients in cohort 4 may be indicative of ‘on-target off-tumour’ MFEζ T cell binding to CEACAM5 antigen present within the lung which would be consistent with the affinity (2.5 nM) of the MFE23 scFV [36] augmented by avidity in CAR T format. The gene discussed is CEACAM5; the disease is neoplasm.