Alexey B. Chukhlovin This issue of CTT begins with a comprehensive review by Professor H.-J. Kolb concerning the role of gut microorganisms, their qualitative and quantitative alterations in the early posttransplant period and current attempts to make their composition and functions more favorable to the host organism. Another mini-review was written by Prof. Tapani Ruutu who draws attention to pharmacokinetics and optimal dosage of busulfan, an old drug which is still routinely used for cytostatic therapy in HSCT. A special survey has discovered some details of its usage in the European clinics. Posttransplant cyclophosphamide-based prophylaxis (PtCy) of acute graft-versus-host disease in leukemic patients is now widely used. However, its introduction to pediatric BMT centers needs further clinical evidence presented by Dr. Bykova et al. who have studied early and late outcomes following PtCy in young patients subjected to HCST for non-malignant diseases Myelodysplastic syndrome (MDS) is intensively studied now because its real incidence seems to be rather common with aging of human population. A meta-analysis performed by Dr. N. Tcvetkov et al. shows some correlations between distinct genetic mutations and clinical response of the MDS patients especially those treated with demethylating agents. A special study by Dr. Khamitova et al. was dedicated to parvovirus B19 which seems to be activated in the patients after cytostatic therapy. Their preliminary data still show correlations between initial parvovirus positivity and subsequent antibody response as well as association with hematological problems occurring after HSCT. The section Experimental Studies contains a review by Prof. A. Yaremenko et al. describing some current and potential applications of artificial scaffolds for craniofacial tissue engineering. Appropriate constructs are made of synthetic polymers which should be cell-friendly, non-cytotoxic and biodegradable upon their implantation. Rather practical and precise approach to sensitive HLA testing in marrow donors using monoallelic Sanger sequencing is shortly presented by Dr. E. Kuzmich et al. Another preliminary, but quite interesting, study is published by Dr. Suat Cheng Tan et al. who suggest a method of culturing adult human brain neurons from surgical samples. This approach has some prospectives and may be potentially developed for regenerative neurology. The Letter to the Editor by Dr. I. Moiseev concerns a practically important issue of individual prognosis in acute myeloid leukemia and role of modern statistics in appropriate predictions based on clinical and laboratory criteria. This is the reply to a comment by Prof. Robert P. Gale published in previous CTT issue. The letter by Moiseev is also accompanied by a response by Prof. R. Gale.