Tacrolimus exposure windows responsible for Listeria monocytogenes infection susceptibility

Abstract

Tacrolimus is widely used to prevent graft rejection after allogeneic transplantation by suppressing T cells in a non-antigen-specific fashion. Global T-cell suppression makes transplant recipients more susceptible to infection, especially infection by opportunistic intracellular pathogens. Infection followed by secondary challenge with the opportunistic intracellular bacterial pathogen, Listeria monocytogenes, was used to probe when tacrolimus most significantly impacts antimicrobial host defense. Tacrolimus-treated mice showed no difference in innate susceptibility following primary infection, whereas susceptibility to secondary challenge was significantly increased. Modifying the timing of tacrolimus initiation with respect to primary infection compared with secondary challenge showed significantly reduced susceptibility in tacrolimus-treated mice where tacrolimus was discontinued prior to secondary challenge. Thus, tacrolimus overrides protection against secondary infection primed by primary infection (and presumably live attenuated vaccines), with the most critical window for tacrolimus-induced infection susceptibility being exposure immediately prior to secondary challenge. These results have important implications for strategies designed to boost antimicrobial T-cell-mediated immunity in transplant recipients.

Keywords: T cell; adaptive immunity; immune suppression; intracellular bacteria; opportunistic infection.

Figure 1.. Tacrolimus selectively impairs immunity against secondary Lm challenge.

(a) Tacrolimus levels in whole blood from mice treated with each dosage for three consecutive days, and 24 hours after the last treatment. (b) Recoverable CFUs in the liver day 3 after primary infection or days 3 after secondary challenge (day 30+3) for tacrolimus treated (10mg/kg per day) compared with no treatment control mice. Data is from at least two independent experiments each with similar results, with each point representing data from an individual mouse. Bar, mean ± SEM.

Figure 2.

Memory CD8+ T cells primed by Lm-OVA infection in tacrolimus treated mice. (a) Percent lysis of OVA_257–264 pulsed compared with unpulsed control donor CD45.1 cells after intravenous transfer into tacrolimus treated compared with no treatment control mice each 30 days after primary Lm-OVA infection. (b) Representative FACS plots and composite data showing the percent OVA-specific CD8+ T cells identified by H-2K^b:OVA_257–264 tetramer staining and total number amongst splenocytes 30 days after primary Lm-OVA infection for tacrolimus treated compared with no treatment control mice. (c) Relative expression of each marker by H-2K^b:OVA_257–264 tetramer staining CD8+ T cells (blue or red) compared with tetramer negative CD8+ splenocytes 30 days after primary Lm-OVA infection for tacrolimus treated compared with no treatment control mice. (d) Relative intensity of H-2K^b:OVA_257–264 tetramer staining by OVA-specific CD8+ T cells and H-2K^b:OVA_257–264 avidity after normalization for levels of T cell receptor (CD3) expression amongst splenocytes 30 days after primary Lm-OVA infection for tacrolimus treated compared with no treatment control mice. (e) Cytokine production after OVA257–264 peptide stimulation compared with no stimulation controls by CD8+ splenocytes 30 days after primary Lm-OVA infection for tacrolimus treated compared with no treatment control mice. Data is from at least two independent experiments each with similar results, with each point representing data from an individual mouse. Bar, mean ± SEM.

Figure 3.

Tacrolimus administration immediately prior to secondary Lm challenge is sufficient for impaired immunity. (a) Schematic outlining when each group of mice are initiated on daily tacrolimus relative to primary infection and secondary challenge. (b) Recoverable CFUs in the liver day 3 after secondary challenge for each group of mice described in panel A compared with no treatment control mice. Data is from at least two independent experiments each with similar results, with each point representing data from an individual mouse. Bar, mean ± SEM.