In the present study, we report the histopathological features, hematological values, and BM cytology of a mouse transplanted with mock-transduced bone marrow, which was found moribund.

The carcinogenic effects of BMT with gene transduced BM via retroviral vector in a C57BL/6 male mouse was presented. The mouse was irradiated at 7.5 Gy from a Cs¹³⁷ source. Transplanted BM cells were originally enriched hematopoietic stem cells isolated from the C57BL/6 male mouse and were transfected with the mock viral vector (empty particle) without any transgene. The tranduced BM cells were administered by tail vein injection at a dose of 35 × 10⁶ cells/kg body weight. Total experimental period was 53 days, but the mouse was found moribund 19 days after BMT and autopsied to evaluate its pathogenesis. Selected hematology, histopathology, and bone marrow cytology measures were evaluated.

Hematological values (Table 1) revealed a decrease in the white blood cells (WBC), red blood cells (RBC), hematocrit, hemoglobin, and platelets, but an increase in reticulocytes.

In BM cytology, a small number of erythroid cells, plasma cells, macrophages, lymphoblasts, lymphocytes etc, were observed, but myeloid cells were almost completely depleted (Fig. 1, Table 2).

In the autopsy findings, red discoloration of subcutaneous, cerebellum, lymph nodes (submandibular and mesenteric), testis, epididymis and gastrointestinal tract were observed. Enlargement of the gall bladder was also noted.

Histopathologically, a severe hemorrhage was seen in cerebellar parenchyma (Fig. 2A). Pulmonary parenchymal cysts were also observed in the lung (Fig. 2B). Hemosiderin deposition, hemorrhage in the heart (Fig. 2C), hepatocellular necrosis and telangiectasia in liver (Fig. 2D) were also detected. Furthermore, hemorrhage and atrophy of seminiferous tubules with necrosis of spermatogenic germ cells were noted in the testis (Figs. 2E and F). Oligospermia and hemorrhage in the epididymis, and atrophy of the BM, thymus, and spleen were observed.

The first successful allogeneic BMT in human was performed in the late 1960s [14]. Science then, BMT has been used with increasing frequency for the treatment of malignant and nonmalignant hematologic diseases, solid tumors, and metabolic and genetic diseases [5]. However, precise regulation of therapeutic gene expression in vivo is still a challenge and the specificity and safety gene therapy needs to be improved even further [13]. Autoimmune-like complication represents a major transplant-related complication initiated by host-reactive T-cells after BMT, and the systemic effects of this initial donor anti-host reaction comprise multi-organ syndrome [6].

CNS hemorrhage is the most prevalent autopsy finding in patient mortality after BMT [2]. In the case reported, an induction of an autoimmune-like complications following BMT was accompanied by severe heart failure with massive myocardial hemorrhage and infiltration by donor-derived CD8-positive cells [12]. Autoimmune-like complications following BMT is also associated with pulmonary edema and cyst formation [14], gonadotoxicity [16], and morphological and functional alterations of thymus [8]. Moreover, autoimmune-like complications remain one of the persistent problems of allogeneic BMT, mostly affecting the skin, gut and the liver [12].

In our case, a large number of infiltrating RBCs were seen in the cerebellar parenchymal spaces, heart, systemic subcutaneous, gastrointestinal tract and liver. Hemorrhage and atrophy of testis and thymus were also observed, and these findings correspond with the previous results mentioned above. There are several factors mentioned in the literature that can be associated with systemic hemorrhage of these multiple organs after BMT. They include a low platelet count or platelet refractoriness underlying BMT [3,15]. And humans with low WBC counts after allogeneic BMT had a significantly higher risk of primary failure of engraftment, or death due to infection, hemorrhage, or graft failure compared to those with higher leukocyte counts [11]. Moreover, it was reported that the BM cytology for allogeneic BM transplanted mice showed displastic BM features in erythroid, myeloid and megakaryocytic cell lineages [15]. In our case, the low platelet and WBC counts in peripheral blood as well as severe depletion of hematopoietic cell in BM were noted. Further studies on cytokine profiles and subsets of leukocytes in blood for specifying the type of autoimmunity may give us more information.