Each <SPECIES>_<GENES>
is a character vector. <SPECIES> is an identifier of species, <GENES> is concatenated three
identifiers of cell type ("TR**" for TCR, "IG**" for Ig), chain (e.g., "**A*" for alpha chains) and gene segment ("***V" for V(ariable) gene segment,
"***J" for J(oining) gene segment, "***D" for D(iversity) gene segment).