To provide a method of alleviating and inhibiting lymphoproliferation syndrome in a mammal.

The pharmaceutical composition for alleviating lymphoproliferation syndrome in a human patient contains as an active ingredient a rapamycin derivative having a chemical structure represented by the formula of Fig. 8 [wherein X is (H, H) or O; Y is (H, OH) or O; R1 is selected from alkyl, thioalkyl and the like; R2 is selected from -H, alkyl and the like; and R4 is methyl or forms a 2-5C alkylene part together with R1]. The lymphoproliferation syndrome is selected from the group consisting of syndromes characterized by proliferation of a B lymphocyte infected with Epstein-Barr virus and malignant lymphoproliferation syndrome selected from the group consisting of after-transplant lymphoproliferation syndrome and B cell lymphoma.