Overexpression of Interleukin-7 Extends the Humoral Immune Response Induced by Rabies Vaccination

Abstract

Rabies continues to present a public health threat in most countries of the world. The most efficient way to prevent and control rabies is to implement vaccination programs for domestic animals. However, traditional inactivated vaccines used in animals are costly and have relatively low efficiency, which impedes their extensive use in developing countries. There is, therefore, an urgent need to develop single-dose and long-lasting rabies vaccines. However, little information is available regarding the mechanisms underlying immunological memory, which can broaden humoral responses following rabies vaccination. In this study, a recombinant rabies virus (RABV) that expressed murine interleukin-7 (IL-7), referred to here as rLBNSE-IL-7, was constructed, and its effectiveness was evaluated in a mouse model. rLBNSE-IL-7 induced higher rates of T follicular helper (Tfh) cells and germinal center (GC) B cells from draining lymph nodes (LNs) than the parent virus rLBNSE. Interestingly, rLBNSE-IL-7 improved the percentages of long-lived memory B cells (Bmem) in the draining LNs and plasma cells (PCs) in the bone marrow (BM) for up to 360 days postimmunization (dpi). As a result of the presence of the long-lived PCs, it also generated prolonged virus-neutralizing antibodies (VNAs), resulting in better protection against a lethal challenge than that seen with rLBNSE. Moreover, consistent with the increased numbers of Bmem and PCs after a boost with rLBNSE, rLBNSE-IL-7-immunized mice promptly produced a more potent secondary anti-RABV neutralizing antibody response than rLBNSE-immunized mice. Overall, our data suggest that overexpressing IL-7 improved the induction of long-lasting primary and secondary antibody responses post-RABV immunization.IMPORTANCE Extending humoral immune responses using adjuvants is an important method to develop long-lasting and efficient vaccines against rabies. However, little information is currently available regarding prolonged immunological memory post-RABV vaccination. In this study, a novel rabies vaccine that expressed murine IL-7 was developed. This vaccine enhanced the numbers of Tfh cells and the GC responses, resulting in upregulated quantities of Bmem and PCs. Moreover, we found that the long-lived PCs that were elicited by the IL-7-expressing recombinant virus (rLBNSE-IL-7) were able to sustain VNA levels much longer than those elicited by the parent rLBNSE virus. Upon reexposure to the pathogen, the longevous Bmem, which maintained higher numbers for up to 360 dpi with rLBNSE-IL-7 compared to rLBNSE, could differentiate into antibody-secreting cells, resulting in rapid and potent secondary production of VNAs. These results suggest that the expression of IL-7 is beneficial for induction of potent and long-lasting humoral immune responses.KEYWORDS IL-7, humoral immunity, rabies virus

Monophosphoryl-Lipid A (MPLA) is an Efficacious Adjuvant for Inactivated Rabies Vaccines

“…Recombinant (r) RABVs were rescued from B7GG cells (kindly provided by Dr. Gang Cao at Huazhong Agricultural University, Wuhan, China) and amplified in BSR cells (kindly provided by Dr. Bernhard Dietzschold at Thomas Jefferson University, Philadelphia, USA) [23]. A dog-derived RABV wild type strain, DRV-Mexico, was isolated from a human patient and propagated in the brains of newborn mice [24,25].…”

“…no. 135206) were utilized to analyze the number of T follicular helper (Tfh) cells in inguinal lymph nodes (LNs) [23]. FITC anti-mouse/human CD45R/B220 antibody (cat.…”

“…RABV-specific total-IgG in serum was determined by enzyme-linked immunosorbent assay (ELISA), as described previously [23]. Sera from mice were collected and inactivated at 56 • C for 30 min.…”

Recombinant Rabies Virus Overexpressing OX40-Ligand Enhances Humoral Immune Responses by Increasing T Follicular Helper Cells and Germinal Center B Cells

“…It has been previously reported that the low and short-lived VNA titers induced by T cell-independent immune responses reached a peak within seven dpi [26]. Recently, the interaction between CD4 + T cells and specialized B cell populations has been reported to be crucial in maintaining a high VNA level for a relatively long time [11]. Previous studies of rRABVs expressing a cytokine such as fms-like tyrosine kinase 3 ligand (Flt3L) showed that the immune factor contributed to enhancing humoral immune responses by mainly recruiting and activating dendritic cells (DCs), resulting in the substantial VNA production [27].…”

“…Additionally, the rRABV expressing a cytokine or a chemokine has been reported to improve the induction of virus-neutralizing antibodies (VNA) by enhancing the immunogenicity [9][10][11]. Therefore, developing affordable live-attenuated rRABV, expressing an immunoregulatory factor, would be a feasible strategic approach to protect animals from rabies.…”