Skip Ribbon Commands
Skip to main content

​Lusso: mRNA-Encoded HIV-1 Env-Gag Virus-Like-Particle (VLP) Vaccines


This study will employ membrane-anchored HIV-1 Envs that naturally engage germline antibodies, and will add two consecutive steps: first, boosts with fully closed autologous Env (tier-2, no glycan holes); and second, boosts with mixed heterologous tier-2 Envs from two different clades. This approach seeks to expand and affinity mature B cell lineages against shared epitopes to produce bNAbs. Combining Env with Gag mRNA will lead to the endogenous production of VLPs. Preliminary results obtained with this approach in a small-scale study showed the development of robust autologous and low-level broadly neutralizing responses against a global panel of tier 2 HIV-1 pseudoviruses. Limited EM analysis showed VRC01 and PG16-like Ab reactivity. In addition, partial protection from a highly virulent heterologous SHIV AD8 intrarectal low-dose virus challenge was seen in seven macaques from two groups of four that received this type of vaccine given by either mRNA alone or by mRNA + protein. Protection correlated with serum Abs to the CD4bs and with ADCC against cells expressing the closed AD8 Env trimer. This investment seeks to confirm and extend these promising initial results in a statistically well-powered vaccine challenge study in rhesus macaques and to define an optimized vaccine formulation and administration schedule for the transition toward clinical studies.

The study will enroll a total of 40 young rhesus macaques, male and female, pre-screened to exclude protective MHC alleles and divided into 4 study arms (n=10 each):

Arm 1: Confirmation of the induction of cross-neutralizing tier-2 bNAbs and protection from heterologous tier-2 SHIV challenge using the same vaccine formulation and immunization scheme used in the original protocol: i) priming with WITO Δ276 Env mRNA (clade B, transmitted/founder, engaging CH01 germline Abs); ii) two consecutive autologous boosts with closed WITO (N276+, glycan repaired); iii) three consecutive heterologous boosts with a mixture of BG505 Env (clade A, glycan repaired) + DU422 (clade C, glycan repaired). All Env mRNA will be co-formulated with SIVmac239 Gag mRNA.

Arm 2: Evaluation of the importance of Gag processing for optimized VLP yield and antigenic configuration using the same Env+Gag mRNA immunogens as in Arm 1, further co-formulated with Gag-Pol mRNA.

Arm 3: Evaluation of an alternative combination of Env immunogens specifically aimed at the induction of bNAbs against the CD4-binding site: i) priming with 426c Δ276 Env mRNA (clade C, transmitted/founder, engaging VRC01 germline Abs); ii) two consecutive autologous boosts with closed 426c (N276+, glycan repaired); iii) three consecutive heterologous boosts with a mixture of BG505 Env (clade A, glycan repaired) + WITO (clade B, glycan repaired). All Env mRNA will be co-formulated with SIVmac239 Gag mRNA.

Arm 4: Naïve macaques (non-immunized) to be used as controls for infection only during the challenge phase.

The current project will develop over a 2-year period, which will encompass the following:

Preliminary phase: The main aims of this phase will be to produce the vaccine and to obtain/screen/quarantine the animals for the study.

Immunization phase: During this phase, sequential inoculations of the mRNA vaccines into the animals will be performed (at intervals of 4-8 weeks), with continuous monitoring for the development of protection-associated immune responses using a variety of assays.

Virus challenge phase: This phase will evaluate the protective efficacy of the vaccine by testing the delay or resistance of vaccinated animals to infection by repeated low-dose mucosal (intrarectal) challenge with a highly virulent, neutralization-resistant heterologous SHIV strain (SHIV AD8, obtained from the laboratory of Malcom Martin and titrated in vivo). Resistance (partial or complete) to this heterologous tier 2/3 strain will provide strong evidence of vaccine efficacy.

Immunological testing phase: In this phase, an extensive characterization of virus-specific immune responses elicited by the vaccine will be completed. A major goal will be to identify correlates of protection from heterologous virus challenge. Furthermore, a comprehensive analysis of Env-specific Ab responses will be performed using single B cell cloning and selection with epitope-specific probes. Specific monoclonal Abs will be derived from probe-sorted B cells, expressed, and their functional and structural properties fully characterized. Their lineage origin and evolution during the immunization process will be analyzed by next-generation sequencing on sequential blood and bone marrow samples.

This grant will be led by Dr. Paolo Lusso at NIAID, in collaboration with Moderna, Inc. and Dr. Andrés Finzi at University of Montreal, Canada.


1. To verify that the results obtained in a previous study with the Env+Gag VLP mRNA platform can be reproduced in a statistically well-powered study (n=10 per study arm).​

2. To verify whether complete and correct Gag processing is a critical requirement for optimal VLP production and quality.

3. To verify whether an alternative Env roster can improve the efficiency and quality of bNAb induction, particularly against the critical CD4 binding site. ​

4. To compare the rate of infection in vaccinated vs. naïve (non-vaccinated) macaques. ​


Grant at a Glance

Principal Investigator

Paolo Lusso, M.D., Ph.D.

Grantee Institution


Project Title

mRNA-Encoded HIV-1 Env-Gag Virus-Like-Particle (VLP) Vaccines

Grant Award

Up to $1.46 million, awarded November 2020

Collaborating Institutions


  • University of Montreal

  • Moderna, Inc.

For general questions about the CAVD or the content of the these pages, please contact
For technical issues with the website, please contact