Leishmania major Infection in Humanized Mice Induces Systemic Infection and Provokes a Nonprotective Human Immune Response

Abstract

Background Leishmania (L.) species are the causative agent of leishmaniasis. Due to the lack of efficient vaccine candidates, drug therapies are the only option to deal with cutaneous leishmaniasis. Unfortunately, chemotherapeutic interventions show high toxicity in addition to an increased risk of dissemination of drug-resistant parasites. An appropriate laboratory animal based model is still missing which allows testing of new drug strategies in the context of human immune cells in vivo . Methodology/Principal Findings Humanized mice were infected subcutaneously with stationary phase promastigote L. major into the footpad. The human immune response against the pathogen and the parasite host interactions were analyzed. In addition we proved the versatility of this new model to conduct drug research studies by the inclusion of orally given Miltefosine. We show that inflammatory human macrophages get infected with Leishmania parasites at the site of infection. Furthermore, a Leishmania -specific human-derived T cell response is initiated. However, the human immune system is not able to prevent systemic infection. Thus, we treated the mice with Miltefosine to reduce the parasitic load. Notably, this chemotherapy resulted in a reduction of the parasite load in distinct organs. Comparable to some Miltefosine treated patients, humanized mice developed severe side effects, which are not detectable in the classical murine model of experimental leishmaniasis. Conclusions/Significance This study describes for the first time L. major infection in humanized mice, characterizes the disease development, the induction of human adaptive and innate immune response including cytokine production and the efficiency of Miltefosine treatment in these animals. In summary, humanized mice might be beneficial for future preclinical chemotherapeutic studies in systemic (visceral) leishmaniasis allowing the investigation of human immune response, side effects of the drug due to cytokine production of activated humane immune cells and the efficiency of the treatment to eliminate also not replicating (“hiding”) parasites.

Humanized Mice as Unique Tools for Human-Specific Studies

“…These inventions cascaded into a series of immunodeficient mice and their variants (BRG, NOG, NRG) (Ali et al 2012; Grover et al 2017; Ishikawa et al 2005; Katano et al 2014; Koboziev et al 2015; Shultz et al 2005) being innovated which enabled in-depth analysis in research areas, such as human hematopoiesis (Rongvaux et al 2011; Yong et al 2016), innate and adaptive immunity (Brehm et al 2010; Pearson et al 2008), autoimmunity (Gunawan et al 2017; Viehmann Milam et al 2014), infectious disease (Keng et al 2015; Lüdtke et al 2015; Wege et al 2012), cancer biology (Chang et al 2015; Her et al 2017; Morton et al 2016), and GvHD (King et al 2008; Kirkiles-Smith et al 2009; Zhao et al 2015), in-turn, facilitating the development of therapeutic agents and novel vaccines. An overview of genotypic and physiological characteristics of each model is outlined in Tables 1 and 2.…”

Humanized Mice, a New Model To Study the Influence of Drug Treatment on Neonatal Sepsis

“…tm1Wjl /SzJ [NSG]) induces the development of a human immune system (6,7) and allows the investigation of human diseases in a small animal model (8)(9)(10)(11). However, some human immune cell populations are weakly present or exhibit functional deficiencies in these mice which mimic the impaired neonatal immune system in many cases.…”

Animal models in biological and biomedical research - experimental and ethical concerns

“…However, in humans, the participation of NO in killing the parasite is still an open question, which has been addressed with the use of "humanized" mice such as the NSG strain that does not have B and T cells from mice, and also presents a higher rate of engraftment with human hematopoietic cells (Wege et al 2012).…”