Melanoma-associated antigen 4 (MAGE-A4) is one of the most common cancer testis antigens in humans. It is expressed in various solid cancers such as synovial sarcoma and is an important therapeutic target for cancer vaccination and autologous T cell therapies such as Afamitresgene autoleucel (Afami-cel).Peptide-loaded MHC MACSimers are offered in various peptide-MHC allele combinations covering a broad range of T cell antigens. MHC MACSimer A*0201 MAGE-A4 can be used for immune response monitoring in cancer patients undergoing (autologous) T cell therapy targeting MAGE-A4, i.e.