Consequences of exposure to ionizing radiation for effector T cell function in vivo

Low-dose radiation therapy for coronavirus disease-2019 pneumonia: Is it time to look beyond apprehensions?

Coronavirus disease-2019 (COVID-19) has become a global health crisis. Mortality associated with COVID-19 is characterized mainly by acute respiratory distress syndrome (ARDS), sepsis, pneumonia, and respiratory failure. The pathogenesis of the disease is known to be associated with pro-inflammatory processes after virus infection. Hence, various therapeutic strategies are being developed to control the inflammation and cytokine storm in COVID-19 patients. Recently, low-dose radiation therapy (LDRT) has been suggested for the treatment of pneumonia/ADRS in COVID-19 patients through irradiation of lungs by gamma/X-ray. In this direction, a few clinical trials have also been initiated. However, a few recent publications have raised some concerns regarding LDRT, especially about possibilities of activation/aggressiveness of virus (severe acute respiratory syndrome coronavirus 2 in case of COVID-19), lung injury and risk of second cancer after low-dose therapy. The present manuscript is an attempt to analyze these apprehensions based on cited references and other available literature, including some from our laboratory. At this point, LDRT may be not the first line of therapy. However, based on existing anti-inflammatory evidence of LDRT, it needs encouragement as an adjuvant therapy and for more multi-centric clinical trials. In addition, it would be worth combining LDRT with other anti-inflammatory therapies, which would open avenues for multi-modal therapy of pneumonia/ARDS in COVID-19 patients. The mode of irradiation (local lung irradiation or whole-body irradiation) and the window period after infection of the virus, need to be optimized using suitable animal studies for effective clinical outcomes of LDRT. However, considering ample evidence, it is time to look beyond the apprehensions if a low dose of radiation could be exploited for better management of COVID-19 patients.

Conditioning regimens for the treatment of experimental arthritis with autologous bone marrow transplantation

Adjuvant induced arthritis (AA) in Buffalo rats is a chronic progressive disease that responds very well to treatment with myeloablation and rescue with autologous BM. These previous results were obtained by conditioning with a lethal single dose of TBI. In the present study various other conditioning regimens were compared with single dose TBI. Fractionated TBI using adjusted total dose was equally effective. CY and BU when used as single agents at the highest tolerated dose were less effective. Combinations of CY (2 x 60 mg/kg) with lower dose (4 Gy) TBI and of BU with CY were as beneficial as high-dose TBI. These results indicate that a very intense reduction of T lymphocytes, in the order of 3-4 log, is required for obtaining the highest rate of long-lasting complete remissions. A similar conclusion was reached from our studies of various conditioning regimens in rats suffering from experimental allergic encephalitis (EAE). If extrapolated to the clinic, such a degree of T lymphocyte eradication poses upper limits to the number of T lymphocytes that can be safely reintroduced with the autograft. The exact limits cannot be derived from these experiments because the addition of autologous T lymphocytes to the graft yielded different results in the two models of autoimmune disease (AID).

Effectiveness and risks of total body irradiation for conditioning in the treatment of autoimmune disease with autologous bone marrow transplantation

The results of experiments with the induced autoimmune diseases adjuvant arthritis and allergic encephalomyelitis in rats, which led to the discovery of the curative effect of autologous bone marrow transplantation following high-dose myeloablative treatment, are reviewed. The rationale is eradication of the autoreactive lymphocytes and memory cells, and the prevention of relapse due to transfer of lymphocytes with the autograft. Comparison of various conditioning regimens in the animal models indicates that a combination conditioning with low-dose total body irradiation (TBI) and high-dose cyclophosphamide is optimal. These findings were the basis for the conditioning currently employed in the treatment of polyarticular juvenile chronic arthritis (JCA) by the teams in Utrecht and Leiden, which consists of cyclophosphamide 50 mg/kg for 4 days, 4 Gy TBI and anti-thymocyte globulin (ATG). The use of TBI for the treatment of non-malignant disease is regarded as undesirable by many physicians in view of the risks, in particular, of growth inhibition in children and the induction of tumours. Experimental and clinical data show that a dose of 4 Gy does not cause significant inhibition of skeletal growth in infants. The risk of excess cancer due to TBI has been well established in quantitative terms and is compared with the expected risk of high-dose cyclophosphamide and the risk associated with the highly immunosuppressive regimens currently used for the treatment of JCA.

In vivo proliferation of naïve and memory influenza-specific CD8(+) T cells

The virus-specific CD8(+) T cell response has been analyzed through the development, effector, and recovery phases of primary and secondary influenza pneumonia. Apparently, most, if not all, memory T cells expressing clonotypic receptors that bind a tetrameric complex of influenza nucleoprotein (NP)(366-374) peptide+H-2D(b) (NPP) are induced to divide during the course of this localized respiratory infection. The replicative phase of the recall response ends about the time that virus can no longer be recovered from the lung, whereas some primary CD8(+)NPP(+) T cells may proliferate for a few more days. The greatly expanded population of CD8(+)NPP(+) memory T cells in the lymphoid tissue of secondarily challenged mice declines progressively in mean prevalence over the ensuing 100 days, despite the fact that at least some of these lymphocytes continue to cycle. The recall of cell-mediated immunity thus is characterized by massive proliferation of the antigen-specific CD8(+) set, whereas the extent of lymphocyte turnover in the absence of cognate peptide is variable, at a low level, and can be influenced by intercurrent infection.

Ionizing radiation modulates the spread of an apathogenic rabies virus in mouse brain

Ionizing radiation has been shown to affect a broad range of viral diseases including neurotropic infections through an immunosuppression mechanism. In the present study we have investigated the effect of ionizing radiation on the characteristics of neurotropic infection by rabies virus, which has the unusual feature of infecting almost exclusively neurons. In order to analyze better the effect produced, the study concerned the spread of an apathogenic rabies virus variant in mouse brain. Irradiation was shown to increase both the intensity and duration of the infection in a reversible and dose-dependent manner and was effective in whole-body irradiation and in head-protected body irradiation, whereas cephalic irradiation had no effect. These results underline the role played by the immune system in the regulation of neurotropic virus infections in the brain and show that phenomena such as viral clearance and time-course of a neurotropic viral infection may be significantly modified by ionizing radiation, even for viruses whose infection involves only neurons.