Erythropoietin Induced Tumour Mass Reduction in Murine Lymphoproliferative Models

leukocyte (PBL) counts begin to increase a few weeks following injection, exceeding 20 ! 10 6 cells/ml. Mice were injected (subcutaneously) with 10 4 MOPC-315 tumour cells in the abdomen area as described [7] . The rHuEPO (epoetin alfa, Eprex®; Janssen-Cilag, Baar, Switzerland) treatment (rHuEPO 30 U) was administered daily for 10 consecutive days, followed by three times per week for an additional 2–3 weeks to the MOPC-315-bearing mice as described [7] . The linear mixed effect (repeated measures) model was used to determine the effect of EPO on tumour size. Variance among mice was taken into account in the analysis by considering the mice to be randomly selected from a larger population. Starting 9 days after tumour cell injection, 28 MOPC315-bearing mice were injected with rHuEPO or albumin (control). The survival curve, shown in fi gure 1 d, demonstrates approximately 50 and 15% survival of the EPOtreated and control mice, respectively, which is in line with our previously documented observations [7] . Tumour growth kinetics in each of the EPO-treated and albumin-treated mice are presented in fi gures 1 a and b, respectively. Statistical analysis of the tumour size of 7 EPO-treated and 11 control progressor mice, which displayed only one localized tumour, using the linear mixed effect (repeated measures) model, yielded an R value of 0.875 ( fi g. 1 c). The predicted mean rate of tumour growth was 0.539 and 1.238 mm/day for EPO and albumin-treatRecombinant erythropoietin (rHuEPO) is widely used in clinical practice in the treatment of several types of anaemia [1–4] . We observed that patients with end-stage multiple myeloma (MM) treated with EPO live longer than expected, despite their original poor prognostic features [5, 6] . BALB/c mice in which MM was induced by transplantation of mineral oil-induced plasmacytoma cells (MOPC-315) showed complete T cell-mediated tumour regression in 30–60% of the animals after treatment with EPO [7] , suggesting that EPO may also act as an antitumour immunotherapeutic agent. Here, we raised a question regarding the effect of EPO on tumour load, rather than on the ultimate survival, by studying two lymphoproliferative murine models, MOPC-315 MM [8] and B cell leukaemia/lymphoma (BCL1) [9] . BCL1 is a B-cell leukaemia/lymphoma that developed spontaneously in a 2-year-old female BALB/c mouse [10] ; its advantage as a model is due to its analogies to human chronic lymphocytic leukaemia/lymphoma. In both models, we focused on tumour-bearing mice that did not achieve complete tumour regression after EPO treatment (‘progressors’). Female inbred BALB/c mice, aged 6–8 weeks, were obtained from the Tel-Aviv University Breeding Center. BCL1 tumour cells (10 4 cells), derived from spleens of tumour-bearing BALB/c mice, were injected intra-peritoneally into syngeneic mice. Typically, peripheral blood Received: January 18, 2005 Accepted after revision: May 9, 2005