Transmission of Toxoplasma gondii Infection Due to Bone Marrow Transplantation: Validation by an Experimental Model

Abstract

Toxoplasmosis is an opportunistic infectious disease and may present a fatal outcome for human bone marrow transplant (BMT) recipients, due to the rapid disease course in immunosuppressed individuals. Several reports about occurrence of toxoplasmosis after BMT have been published in the literature, but this disease has been associated mainly due to reactivation of latent infection rather than primary infection. Even though there are reports of acute toxoplasmosis in recipients who were seronegative for T. gondii, suggesting transmission of infection after BMT, the source of infection in those cases has not been clearly demonstrated, whether it is due to the transplantation procedure by itself or from environmental source. Thus, the present study aimed to observe if it could be possible to demonstrate the parasite's ability to infect bone marrow (BM) cells and cause toxoplasmosis, when using an experimental model. Our results showed that 11% of hematopoietic and 7.1% of nonhematopoietic lineages may become infected when using in vitro experiments. Also, in vivo experiments demonstrated that, when C57BL/6 mice were infected with RH-RFP or ME-49-GFP T. gondii strains, the BM cells may be infected at different time points of infection. The parasites were detected by both fluorescent microscopy and qPCR. Also, when those BM samples were collected and used for BMT, the transplanted animals presented high rates of mortality and 87.5% of them became seropositive for T. gondii. Taken together, our results clearly demonstrated that it is possible to acquire primary T. gondii infection from the donor cells after BMT. Therefore, we are emphasizing that, before transplantation, serological screening for T. gondii infection from both donors and recipients, in addition to DNA search for this parasite from donor bone marrow cells, are necessary procedures to avoid the risk of T. gondii infection for immunocompromised patients.

Keywords: Toxoplasma gondii; acute infection; bone marrow; infectious diseases; reactivation; toxoplasmosis; transplantation.

Figure 1

Flow cytometry analysis of BM cells co-cultured with ME-49-GFP T. gondii strain stained with anti-CD45 (APC-Cy7). (A) CD45(APC-Cy7)/ME49 (GFP) gate from control cells (B) CD45(APC-Cy7)/ME49 (GFP) gate from infected cells.

Figure 2

Assessment of parasite in bone marrow samples. Microscopic images of bone marrow cell from donors at different times of infection. Mice infected with RH-RFP at 3 days post infection (A), 5 days post infection (B), and 7 days post infection (C). Mice infected with ME49-GFP at 3 days post infection (D), 5 days post infection (E), 7 days post infection (F), 15 days post infection (G), and 30 days post infection (H). Arrows indicate the parasite presence. (I) Quantitative real-time PCR analysis of the T. gondii burden in BM samples from murine donors.

Figure 3

Evaluation of T. gondii infection in animals after bone marrow transplantation. (A) Levels of IgG antibodies anti-Toxoplasma gondii in serum samples of transplanted mice after 10 days of BMT. The values are expressed in ELISA index and dashed line indicates the cut off value = 1.2. (B,C) Survival curve of mice after BMT. (D) Representative image of bone marrow cells from recipient mice transplanted with BM from animals infected with ME-49-GFP after 30 days of BMT. (E) Representative image of bone marrow cells from recipient mice transplanted with BM from animals infected with RH-RFP after 21 days of BMT. Arrows indicate the parasite presence. Cropped image a zoom of cells infected.