Reduced perilesional lymphocytic infiltration of an invasive carcinoma of the vulva in ICOS deficiency. Paraffin sections of the carcinoma of the vulva of patient 1 demonstrate a reduced infiltration of lymphocytes at the site of invasion. CD4⁺ T cells were especially diminished compared with an immunocompetent control patient. The number of CD8⁺ T cells was comparable.