Patient-derived xenografts (PDX) are being increasingly utilized in preclinical oncologic research. Maintaining large colonies of early generation
tumor-bearing mice is impractical and cost-prohibitive. Optimal methods for efficient long-term cryopreservation and subsequent reanimation of PDX
tumors are critical to any viable PDX program. We sought to compare the performance of "Standard" and "Specialized" cryoprotectant media on various cryopreservation and reanimation outcomes in PDX
tumors. Standard (10%
DMSO media) and Specialized (Cryostor®) media were compared between overall and matched PDX
tumors. Primary outcome was reanimation engraftment efficiency (REE). Secondary outcomes included time to
tumor formation (TTF), time to harvest (TTH), and potential loss of unique PDX lines. Overall 57 unique PDX
tumors underwent 484 reanimation engraftment attempts after previous cryopreservation. There were 10 unique PDX
tumors cryopreserved with Standard (71 attempts), 40 with Specialized (272 attempts), and 7 with both (141 attempts). Median frozen time of reanimated
tumors was 29 weeks (max. 177).
Tumor pathology, original primary PDX growth rates, frozen storage times, and number of implantations per PDX model were similar between cryoprotectant groups. Specialized media resulted in superior REE (overall: 82 vs. 39%, p < 0.0001; matched: 97 vs. 36%, p < 0.0001; >52 weeks cryostorage: 59 vs. 9%, p < 0.0001), shorter TTF (overall 24 vs. 54 days, p = 0.0051; matched 18 vs. 53 days, p = 0.0013) and shorter TTH (overall: 64 vs. 89 days, p = 0.009; matched: 47 vs. 88 days, p = 0.0005) compared to Standard. Specialized media demonstrated improved REE with extended duration cryostorage (p = 0.048) compared to Standard. Potential loss of unique PDX lines was lower with Specialized media (9 vs. 35%, p = 0.017). In conclusion, cryopreservation with a specialized cryoprotectant appears superior to traditional laboratory-based media and can be performed with reliable reanimation even after extended cryostorage.