In vivo Myeloid Cell Purging (MYP) as a therapeutic tool in MDR HIV patients

H. Hasson*, B. Mantelli*, M. Malnati°, A. Vecchi, A. Saniabadi#, A. Lazzarin*, A. Beretta*, P. Biswas*

*Clinic of Infectious Diseases, °Unit of Human Virology, San Raffaele Scientific Inst., Milano (Italy); #ImmunoResearch Institute, Takasaki (Japan)

Background: Multi-drug resistance (MDR) is a common problem arising upon HAART. Structured treatment interruptions (STI) are sought as a mean to induce reversion to wildtype genotype. We performed a study with 12 MDR patients (pts): 6 underwent STI alone (CTRL) and the other 6 STI along with myeloid cell purging (MYP). MYP is a procedure (six consecutive sessions, 1/weekly) that selectively traps monocytes and granulocytes and has proven beneficial in the treatment of several inflammatory diseases. MYP has previously been tested on HIV-infected pts resulting safe and associated with an increase of CD4+ T lymphocytes. Material and Methods: Whole blood is collected prior (Pre) and immediately after (Post) each MYP session for haematologic assessments. An aliquot of blood undergoes peripheral blood mononuclear cell (PBMC) separation. We studied several time points, focusing on T0, T14 and T35 (first, third and last MYP session, respectively). Blood is periodically withdrawn also from CTRLs. Cell-associated HIV load is measured with a specific and sensitive real-time PCR assay which also normalizes the cellular content of each sample through a second real-time PCR assay. Results: No major differences in terms of viremia and CD4 counts occurred between MYP pts and CTRLs during the MYP period. Nevertheless, at HAART reintroduction 5/6 MYP pts reached and still maintain undetectable viremia for over an year from the time of reintroduction. The 6th MYP pt maintains low viremia (1000 copies/ml). Conversely 4/6 CTRLs did not reach undetectable viremia. Moreover, all MYP pts, but none of CTRLs, displayed a persistent recovery of CD4 counts >500 cells/µl. Each patient showed its own profile of monocyte depletion achieved by MYP, with an average of 30% among all pts and all MYP sessions. When the ratio of monocytes in Post and Pre samples is kinetically plotted against the ratio of PBMC-associated HIV load in the same Post and Pre samples, striking graphs appear. Almost perfect overlapping occurs in three MYPpts, whereas in the other 3 there is an inverse trend between the two parameters. Interpretation of the diagrams of each MYP pt leads to provocative speculation on whether the PBMCassociated virus is preferentially associated to lymphocytes or monocytes and on how this association appears to change during the course of MYP. We are planning cellular purifications and genotyping of the virus to document the interesting findings of this study. Conclusions: MYP is a safe procedure that greatly improves the outcome of STI in MDR pts. The mechanisms of action are certainly complex, but worth studying.