INCLUSION CRITERIA FOR ENROLLMENT: The patient has been off all immunosuppression for at least weeks at the time of PTCy-MILs collection EXCLUSION CRITERIA FOR ENROLLMENT: The use of immunosuppression for grade II-IV acute GVHD within days prior to the infusion of PTCy-MILs INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Confirmation of active relapse involving the bone marrow of a hematologic malignancy >= months after alloHCT employing PTCy as GVHD prophylaxis and more than days after PTCy-MILs infusion INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Donor CD+ chimerism >= % measured in peripheral blood or bone marrow INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Eastern Cooperative Oncology Group (ECOG) performance status =< or Karnofsky performance scale (KPS) >= % INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: No active acute infections INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: No requirement for systemic steroids INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: White blood cell count (WBC) >= ,/uL INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Absolute neutrophil count (ANC) >= ,/uL INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Platelets >= ,/uL (transfusions are permitted) INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Hemoglobin >= . g/dL (transfusions are permitted) INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: AST (aspartate aminotransferase) =< x ULN INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: ALT (alanine aminotransferase) =< x ULN INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Bilirubin =< . x ULN INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Serum creatinine =< . x ULN or creatinine clearance (CrCl) >= mL/min (if using the Cockcroft-Gault formula) INCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Expectation of ability to safely undergo salvage treatment appropriate for the patients malignant disease type EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: More than years have elapsed since the patients initial PTCy-MILs infusion EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Most recent alloHCT performed did not utilize PTCy GVHD prophylaxis EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: The presence of active GVHD requiring treatment EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: The use of immunosuppression for grade II-IV acute GVHD within days prior to the infusion of PTCy-MILs EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Creatinine >= . EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: Total bilirubin > times the upper limit of normal (ULN) EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: AST (aspartate aminotransferase)/ALT (alanine aminotransferase) > times the ULN EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: HIV-/ or HTLV-/ positivity EXCLUSION CRITERIA FOR ADDITIONAL PTCy-MILs INFUSION AT RELAPSE: The patients life expectancy is =< days even with aggressive treatment and/or supportive care, as determined by the treating hematologist/oncologist