This presentation offers a comprehensive overview of the development of HIV vaccines, covering the scientific, clinical, and public health perspectives necessary for students and professionals in microbiology, infectious diseases, and immunology. Key highlights include: Structure and replication of HIV (Lentivirus - Retroviridae) HIV genes: Tat, Nef, Rev, Vif, Vpu, Vpr, LTR, and their role in immune evasion Types of vaccines: Live-attenuated, DNA, mRNA, viral vector, protein subunit, nanoparticle-based Historical vaccine efforts: From gp120 subunit to recombinant Ad5 vector-based designs Analysis of major trials: RV144, STEP, HVTN 702, Imbokodo India’s contributions: NARI vaccine trials on HIV-1 subtype C Challenges: High mutation rate, viral integration, lack of effective animal models, and ethical concerns Novel directions: Broadly neutralizing antibodies (bNAbs) and vectored immunoprophylaxis Backed by leading literature from NIH, NARI, CDC, WHO, and peer-reviewed journals, this slide deck is ideal for: Postgraduate students and academic presentations Faculty lectures in medical microbiology or immunology Clinical updates in infectious disease departments Public health policy and awareness campaigns

1. HIV Vaccine

2. References
• Kaur A, Vaccari M. Exploring HIV Vaccine Progress in the Pre-Clinical and
Clinical Setting: From History to Future Prospects. Viruses. 2024 Feb
27;16(3):368
• Hargrave A, Mustafa AS, Hanif A, Tunio JH, Hanif SNM. Current Status of
HIV-1 Vaccines. Vaccines (Basel). 2021 Sep 16;9(9):1026
• Plotkin’s vaccine-7th
edition, Chapter-29, HIV vaccines

3. Layout Introduction to HIV & AIDS
What is Vaccine?
Types of vaccines
Vaccine development history
The need for HIV vaccine
Challenges in HIV vaccine development
History of HIV vaccine research
Phase 3 HIV vaccines
Ongoing HIV vaccine trials
HIV vaccine trials in India
Types of HIV vaccines in research
Vaccine hesitancy
conclusion

4. Introduction to HIV and AIDS
• Genus- Lentivirus
• Family- Retroviridae
• Reverse transcriptase

6. Tat is a transcriptional transactivator gene, i.e. essential for HIV-1 replication
Nef (negative factor gene, p27): down-regulates the CD4 expression on the host cell surface
and increases viral infectivity
Rev (regulator of virus gene): It enhances the expression of structural proteins
Vif (viral infectivity factor gene): It influences the infectivity of viral particles
Vpu gene: It promotes the CD4 degradation and release of progeny viruses from the host cell
and are type type-specific; expressed only by HIV-1
Vpr gene: It increases the transport of viral genome into the nucleus and also arrests host
growth
LTR (long terminal repeat) sequences are present on both ends and provide promoter,
enhancer, and integration signals.
regulate viral replication and are important in disease pathogenesis in vivo.

7. What is a Vaccine?
• A substance that teaches the body how to recognize and protect itself against a
disease-causing agent
• Vaccines stimulate the immune system to recognize and fight pathogens.
• Goal: Prevent infection or reduce disease severity.
The body is exposed
to a substance
designed to elicit an
immune response
The immune system
mounts an immune
response and
‘memory’ against the
pathogen
If the immune
system is
exposed to the
pathogen again,
it will be
prepared to
prevent and/or
control infection

9. Types of Vaccines
• Live-Attenuated Vaccines: Contain weakened (attenuated) forms of the pathogen.
Elicit a strong, long-lasting immune response.
Examples: Measles, Mumps, Rubella (MMR), Chickenpox, Oral Polio Vaccine(OPV).
• Inactivated Vaccines: Contain killed (inactivated) forms of the pathogen.
Safer for immunocompromised individuals but may require booster doses.
Examples: Inactivated Polio Vaccine (IPV), Hepatitis A, Rabies.
• Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines: Use specific parts of
the pathogen (e.g., protein, sugar, or capsid).
Safe and suitable for immunocompromised individuals.
Examples: Hepatitis B, HPV, Pneumococcal, Meningococcal, Hib

10. • Toxoid Vaccines: Contain inactivated toxins (toxoids) produced by the pathogen.
Target diseases caused by bacterial toxins.
Examples: Diphtheria, Tetanus.
• mRNA Vaccines: Use messenger RNA to instruct cells to produce a protein that
triggers an immune response.
Fast to develop and highly effective.
Examples: COVID-19 vaccines (Pfizer-BioNTech, Moderna).
• Viral Vector Vaccines: Use a harmless virus (vector) to deliver genetic material
from the pathogen to stimulate an immune response.
Examples: COVID-19 vaccines (AstraZeneca, Johnson & Johnson), Ebola vaccine.

11. • DNA Vaccines (under development): Use DNA plasmids to instruct cells to
produce pathogen antigens and trigger immunity.
Examples: Some experimental vaccines for COVID-19 and Zika virus.
• Protein Subunit Vaccines: Use fragments of the pathogen's protein to elicit an
immune response.
Examples: Novavax COVID-19 vaccine.
• Whole-pathogen vaccines (emerging technologies): Use the entire pathogen in its
natural or modified state to elicit immunity.
Examples: Traditional methods include live-attenuated and inactivated vaccines.
• Nano-particle-based vaccines (experimental): Use engineered nanoparticles to
mimic pathogens and stimulate an immune response

12. What does the virus do to our
immune system?
The virus attacks specific lymphocytes called
“T helper cells” (CD4 cells, also known as T-
cells), taking over the machinery of these cells
to make more copies of itself. This process
begins to destroy the CD4 cells.
Over time, the total number of CD4 cells in
the body drops off, lowering the body's
resistance to invading diseases causing
opportunistic infections

13. So what does the AIDS vaccine
aims to do?
Infected
helper T cell
Killer T cell
Killer T cells could eliminate
infected helper T cells,
before the virus can spread
Antibodies could block HIV
from entering helper T cells
Humoral immune response Cellular immune response

14. The Need for an HIV Vaccine
•Antiretroviral Drugs (ARVs):
• Effective in treating HIV-1 infections.
• Used as PrEP to prevent infections in at-risk populations.
• A milestone in scientific progress.
•Challenges:
• ARVs are not a replacement for a vaccine.
• ~90% of HIV-1 cases are in developing countries.
• Limited access to ARVs in resource-poor settings.
A vaccine is essential to end the HIV epidemic globally.

15. Vaccine Development in History

16. 45 years after the discovery of HIV/AIDS, medical research still failed to invent an
effective approved vaccine. This is attributed to various factors:
• High mutability of the virus is the single most important factor
• Diverse antigenic types & subtypes/clades globally.
• The concept of live attenuated or even killed vaccine is impracticable due to the
possible risk of reactivation
Challenges in HIV Vaccine Development

17. • Long latent period between exposure and appearance of symptoms
• Lack of ideal small animal models for studying HIV infection
• Ethical issue: Difficulty to get human volunteers for HIV vaccine trial
• Natural immunity fails to clear HIV as it targets cells of the immune system
• As HIV is a retrovirus: The viral genome soon gets integrated into the host
cell genome. Hence, it provides a short window of opportunity to control.

18. • HIV shows extensive antigenic diversity because it undergoes high rates of mutation.
• This is believed to be due to the error-prone nature of the reverse transcriptase enzyme
• Although mutations may occur in any genes, most notably it is observed in the env gene
• Unfortunately, envelope proteins are the major target against which antibodies are produced.
Hence mutations in the env gene are the main reason which explains why:
• HIV evades the host's immune response
• Vaccination against HIV is extremely difficult.
High Mutability

19. Based on sequence differences in the env gene, HIV comprises two serotypes HIV-1 and 2.
HIV-1
• It is divided into 4 groups (M, N, O, P).
• 'M' is the dominant group worldwide.
• It comprises of ten subtypes or "clades" (A-J)
• Subtypes are sometimes further split into sub-subtypes such as A 1 and A2 or Fl and F2
• There are also "circulating recombinant forms" or CRFs derived from recombination
between different subtypes.
(CRF0l-AE is a recombination between subtypes A and E)
HIV- antigenic types & subtypes

21. HIV-1 subtypes or clades do not vary in pathogenesis or biology, they differ in geographical
distribution and transmission.
Geographical distribution
• Subtype A is common in West Africa
• Subtype B is predominant in Europe, America, Japan, and Australia
• Subtype C is the most common form worldwide (47%). It is also the dominant form in
Southern and Eastern Africa, India, and China
• Greatest diversity: In Cameroon (West Africa}, all known HIV groups and subtypes are
found. It is probably, considered as the place of origin of the virus.
Transmission: Asian and African subtypes (C and E) are more readily transmitted
heterosexually, whereas American strains (subtype B) preferentially spread through blood
and homosexual contact.

22. HIV-2
It comprises of eight groups (A- H)
The same infected host may have a group of closely related viral subtypes and/or CRF
at a given time which are collectively called quasispecies

23. Animal Models in HIV Vaccine Research
•Early Challenges:
• Chimpanzees could contract HIV but did not mimic human disease progression.
•Development of SHIV Model:
• SHIV: A chimeric virus combining gag and pol genes from SIV and env gene from
HIV.
• Created a more pathogenically relevant model to aid vaccine research.
•Current Standard Model:
• Macaque monkeys infected with low-dose SHIV intravaginally.
•Limitations of the Model:
• SHIV models do not fully replicate human disease pathology or immune responses.

24. •Funding for HIV vaccine research has declined since 2010.
•The US government and the Bill & Melinda Gates Foundation have
contributed 85% of the funding.
•In 2018, these two entities provided a combined total of $680 million.
•This limited financial backing hinders progress in HIV vaccine research.
Funding

25. Preventive vaccines
Designed for people who are not infected with
HIV, to:
reduce the risk of infection, reduce viral load
following infection, allowing the body to
control the disease better.
Therapeutic vaccines
Designed for people who are living with
HIV, to:
train the body’s immune system to help
control HIV in the body
1.VRC01
2.ALVAC-HIV (vCP1521)
3.TheraMAB
4.Tat Vaccines
5.Imbokodo
6.HIV-1 DNA Vaccine (DNA-
MVA)
7.FELIX Vaccine (Fos-elicited
Immune eXpression)
8.cAd3-HIV
•RV144
•HVTN 702
•Imbokodo
•AD26.Mos.HIV
•VRC01
•ALVAC-HIV (vCP1521)
•IAVI HIV Vaccine
•Quil-A
•TG1050
•GSK's MVA-B

26. In 1984, after it was confirmed that HIV caused AIDS, the United States
Health and Human Services Secretary Margaret Heckler declared that a vaccine
would be available within two years.
The NIH played a significant role in funding and supporting HIV vaccine research
through its National Institute of Allergy and Infectious Diseases (NIAID).
In 1987, Dr. Robert Gallo and his team at the NIH were among the first to begin the
initial exploration of potential vaccines. This Phase 1 trial enrolled 138 healthy, HIV-
negative volunteers
History of HIV vaccine research

27. History of HIV vaccine research
•Late 1980s: Initial HIV vaccine efforts focused on inducing neutralizing antibodies and
cytotoxic T lymphocyte responses for protection.
•Target Proteins: Vaccines targeted gp120 or gp160 envelope proteins of HIV-1.
•Inspiration: The approach is based on the success of the recombinant hepatitis B
vaccine in producing neutralizing antibodies.
•Outcome: The approach failed; VaxGen trials (2003) testing gp120 vaccines showed
poor results, leading to its discontinuation
From 1987 to 2021, there have been three major approaches driving HIV-1 vaccine development

28. •Second Approach: Focused on using a viral vector to induce a
CD8+ T cell response.
•Rationale: Researchers in the early 2000s observed that CD8+
T cells were critical in controlling HIV infection, as their
depletion led to loss of immune control.
•Goal: To control post-infection viremia and potentially prevent
HIV acquisition.
•Mechanism: Recombinant vectors with HIV genes were used to
produce HIV proteins, presented to the immune system via the
Class I antigen-presenting pathway.
•Outcome: This approach ended after the STEP trial was
terminated

29. •STEP Trial (2004) and Phambili Trial (2007): Early T-cell-based HIV vaccine
candidates.
•Vaccine Design: Used a recombinant Ad5 vector with HIV-1 clade B gag/pol/nef
inserts (no envelope genes).
•Purpose: Targeted the virus core to elicit immune responses against proteins and DNA
within the virus.
•Outcome: Trials ended prematurely due to lack of efficacy and failure to reduce viral
load in participants.
•Adverse Findings: Participants with Ad5-neutralizing antibodies or those
uncircumcised had a higher risk of HIV infection compared to the placebo group.
•Conclusion: An example of vaccine product failure.

32. Current Approach: Utilizes a heterologous prime-boost strategy to elicit both
humoral and cell-mediated immune responses.
Prime-Boost Strategy:
•Priming: With a virus.
•Boosting: With a recombinant protein.
•Heterologous vs. Homologous: Heterologous uses the same antigens in different
vaccine types and is more immunogenic than homologous series (e.g., DTP).
1. The prime and boost use different vaccine types that deliver the same
antigen.
2. More immunogenic than the homologous approach.
3. Example: Priming with a viral vector and boosting with a recombinant
protein vaccine.

33. Advantages:
•Enhances immune response (humoral and cellular).
•Induces neutralizing antibodies.
•Produces unique populations of effector-like memory T cells targeting non-lymphoid
organs.
Outcome Factors: Dependent on antigen, vector type, delivery route, dose, adjuvant,
schedule, and immunization sequence.
Clinical Success: Employed in the RV 144 trial, the only modestly successful HIV
vaccine trial to date (results released in 2009).

34. RV 144 HIV Vaccine Trial
•Prime: Canarypox viral vector expressing HIV antigens.
•Boost: Recombinant gp120 protein vaccine.
•Outcome: Showed modest efficacy (~31%), demonstrating proof-of-concept for the
prime-boost approach

36. HIV vaccines - Phase 3 clinical trials
1. ALVAC-HIV (vCP1521) and AIDSVAX (gp120 vaccine)
•Phase 3 Trial: VAX003 (1999-2003) and VAX004 (1999-2003)
•Vaccine Type: Combination of a Canarypox vector (ALVAC-HIV) and a recombinant
gp120 protein (AIDSVAX).
•Outcome: Both trials showed no significant protection against HIV infection.
•Impact: The combination of a vector and protein approach was a pioneering attempt but
ultimately unsuccessful.
2. Step Trial (2004-2007)
Vaccine: Recombinant Adenovirus Type 5 (Ad5) vector with HIV-1 gag, pol, and nef genes
3. HVTN 702 Trial (2016-2020)
•Vaccine: ALVAC-HIV and AIDSVAX (based on RV144).

38. Ongoing HIV-1 clinical trials

40. NARI HIV Vaccine Trials (National AIDS Research Institute)
•Early trials conducted in India to develop vaccines targeting HIV-1 subtype C, which
is prevalent in India.
•First trials included modified vaccinia Ankara (MVA) and Adeno-Associated
Virus (AAV) vector-based vaccines.
HIV vaccine trials in India
AAV-Based HIV Vaccine Trial
•Year Started: 2006
•Phase: I
•Vaccine Name: AAV-based HIV-1 subtype C vaccine
•Molecular Basis: An adeno-associated virus vector designed to deliver HIV-1 subtype C
genes to elicit an immune response.
•Outcome: Conducted by NARI. The vaccine was safe, but the immune responses were
insufficient to justify progression to later trial phases.

41. Modified Vaccinia Ankara (MVA) Vaccine Trial
•Year Started: 2003
•Phase: I
•Vaccine Name: MVA-based HIV-1 subtype C vaccine
•Molecular Basis: A live attenuated MVA vector engineered to express HIV-1
subtype C antigens, aiming to induce immune responses specific to the prevalent
HIV strain in India.
•Outcome: The vaccine was found to be safe; however, detailed immunogenicity
results were not promising enough to proceed to further phases.

42. tgAAC09 Vaccine
•Year Started: 2005 Phase: I
•Molecular Basis: A recombinant adeno-associated virus serotype 2 (AAV2)
vector-based vaccine targeting HIV-1 subtype C, the predominant strain in India.
•Outcome: The trial was conducted to assess safety and immunogenicity. While the
vaccine was found to be safe, it elicited only modest immune responses, leading to
the discontinuation of further development.
DNA/MVA Prime-Boost Approach
•NARI also tested a DNA vaccine (ADVAX) as a primer, followed by an MVA
vaccine boost to enhance immune response.
•Focused on safety, immunogenicity, and boosting the immune response.

43. • Broadly neutralizing antibodies (bNAbs) – specialized antibodies that bind to and
neutralize multiple strains of HIV.
• BNAbs inhibit the virions from entering the host cells, preventing HIV
integration into the genome
•Objective: Assess if bNAbs induce protective immune responses in HIV-1 patients.
•Trials Conducted:
•Caskey et al.: Passive infusion of 3BNC117 in HIV-1 patients without HAART.
•Lynch et al.: VRC01 infusion in HAART-treated and untreated HIV-1 patients.
•Outcomes: Both 3BNC117 and VRC01 infusions reduced viral load in HIV-1 patients
not on HAART.
•Future Research: Necessary to develop active immunization strategies using bNAbs

44. •Challenges of Passive bNAb Therapy
Difficult to administer due to health infrastructure constraints.
High cost of biological production.
•Active Vaccination Advantage
Eliciting bNAbs through active vaccination is more effective as a prophylactic measure.
•Vectored Immunoprophylaxis Concept
Involves injecting an adeno-associated viral vector carrying bNAb genes into the muscle.
Designed to address the challenges of passive immunotherapy

45. These trials represent incremental progress in the pursuit of effective HIV vaccines, with
lessons learned from each contributing to the refinement of immunogen design and
delivery methods.

47. Conclusion
– HIV remains a major global health challenge.
– Vaccines are critical for controlling the epidemic.
– Significant progress made, but challenges remain.
– Continued research and innovation are essential.