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FCUL 3.2 Imunologia > Vacinação > Flashcards

Flashcards in Vacinação Deck (27)
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1

O que é uma vacina?

• A palavra vacina deriva do latim Variolae vaccinae (Varíola bovina), que em 1798 Edward Jenner demonstrou ser eficaz na prevenção da Varíola em humanos.

• Atualmente o termo vacina é aplicado a todas as preparações biológicas, produzidas a partir de microrganismos vivos, que aumentam a imunidade contra a doença causada por esse microrganismo (vacina profilática), ou nalguns casos curam a doença (vacina terapêutica).
-> o objetivo de uma vacina profilática é induzir imunidade protetora de longa duração.

2

Desenvolvimento de uma vacina

• Investigação básica intensiva
-> Requer muito tempo e dinheiro
-> Delineação prévia dos alvos imunológicos específicos do programa de
vacinação (correlatos de proteção imune).

• Ensaios clínicos envolvendo humanos são estritamente regulamentados

• Mesmo que uma vacina eficaz seja encontrada, a presença de efeitos adversos impede a utilização da mesma

• Nas vacinas, a proteção é providenciada quer por componentes préexistentes
da resposta imunológica ou mais frequentemente, por
indução da geração de células de memória específicas para um determinado antigénio. A imunização pode ser assim dividida em passiva e ativa:
-> Passiva- via transferência de Ab
-> Ativa- induz proteção duradora, envolve formação de células de memória

3

Imunização passiva

Imunização passiva é temporária (semi-vida dos Abs)
• Eficaz para a recuperação de
indivíduos infetados com determinados microrganismos
• Para imunidade duradora é
necessário proceder a uma
imunização ativa
• Plasma convalescente usado para tratamento de infeção severa por SARS-Cov2

Common agents:
-Horse antivenin (black widow spider bite, snake bite)
-Horse antitoxin (Botulism, Diphteria)
-Human polyclonal Ab (CMV, varicella zoster virus)
-Pooled human Ig (Hepatitis A and B, Measles, tetanus)
-Human or horse polyclonal Ab (Rabies)
-Monoclonal anti-RSV (respiratory disease)

4

Objetivo da vacinação

Primary immune response: fairly weak and short lived (first encounter with antigens from a pathogen; seen in a nonpathogenic form. memory T-cells and B-cells are generated.)

Secondary immune response: strong and longer lasting (subsequent encounter with the actual pathogen; because memory cells are already present as a result of vaccination, a secondary immune response occurs on first encounter with the pathogen)

5

Herd Immunity (imunidade de grupo)

• Herd immunity é a proteção da comunidade que é atingida quando uma percentagem elevada da população está vacinada (imune), limitando
assim a propagação da doença infecciosa. Garante assim uma barreira protetora, especialmente para aqueles indivíduos que não podem ser
vacinados. Estes incluem grupos vulneráveis tais como bebés demasiado jovens para ser vacinados, indivíduos com alergia severa a componentes
da vacina e indivíduos imunocomprometidos.

-> O threshold de imunidade de grupo é atingido quando o número de indivíduos imunes na população é suficiente para que a doença deixe de persistir na comunidade

• O nível de cobertura de vacinação necessário para que a transmissão da doença
seja interrompida depende da facilidade com que a doença é transmitida e da eficácia da vacina em estimular a imunidade

6

Threshold de imunidade de grupo de algumas vacinas (ver quizlet!)

• The table shows the HIT for several diseases. Measles and pertussis are highly contagious airborne diseases and a larger share of people need to be vaccinated to stop the transmission. Because of this, these diseases have the highest HIT rates that need to be reached. For example, two doses of measles vaccination offers 99% protection, while in the absence of immunization, the lifetime risk of infection is nearly 100%.

* Rt (índice de transmissibilidade): número de casos produzidos por cada indivíduo infetado


SARS: Airborne droplet: Rt 2-5: Herd immunity threshold 50-80%
- restantes em quizlet!!

7

Devenvolvimento + eficácia de vacinas

Desenvolvimento de vacinas
• Imunidade protetora tem que ser atingida
-> Mecanismo de proteção contra infeção natural tem que ser tido em atenção
• Tem que produzir memória imunológica
-> Vacina que induz apenas resposta imunológica primária (mas não secundária) não é eficiente

Eficácia de vacinas
• Vacinas existentes induzem geração de Ab protetores, mas são menos eficientes em promover o desenvolvimento de imunidade celular
(dependente do tipo de vacinas)

Vacinas são mais eficientes contra microrganismos que:
- Não variem Ag de superfície
- Não possuam reservatórios animais
- Não estabeleçam infeções latentes nas células do hospedeiro
- Não interfiram com a resposta imunológica do hospedeiro

8

Doenças para as quais vacinas eficientes são ainda necessárias

malaria, schistosomiasis, intestinal worm infestation, tuberculosis, diarrheal disease, respiratory infections, HIV/AIDS, measles (*Current measles vaccines are effective but heat-sensitive, which makes their use difficult in tropical countries; heat stability is being improved.)

Factors required for a successful vaccine:
-effectiveness
-availability
-stability
-cheapness
-safety

9

Pipeline para desenvolvimento de uma vacina

Traditional vaccine development can take 15 years or more, starting with a lengthy discovery phase in which vaccines are designed and exploratory preclinical experiments are conducted.

This is usually followed by a phase in which more formal preclinical experiments and toxicology studies are performed and in which production processes
are developed.

During this process an investigational new drug (IND) application is filed and the vaccine candidate then enters phase I, II and III trials.

If, when phase III trials are completed, the predetermined end points have been met, a biologics licence application (BLA) is filed, reviewed by regulatory agencies and finally the vaccine is licensed. After that point, large-scale production begins.

10

Tipos de vacinas

1ª geração (whole organisms!)
---Live attenuated (measles, mumps, polio, rotavirus, rubella, tuberculosis, varicella, yellow fever) -->
+ strong immune response, often lifelong immunity with few doses;
- required refrigerated storage, may mutate to virulent form

---Inactivated or killed (cholera, influenza, hep A, plague, polio, rabies, zika) -->
+ stable, safer than live vaccines, no refrigerated storage
-weaker immune response than live vaccines, booster shots usually required


2ª geração (purified macromolecules!)
---toxoid (inactivated exotoxin) (dipheria, tetanus)
+immune system becomes primed to recognize bacterial toxins
-may require booster shots

---subunit (hep B, pertussis, streptococcal pneumonia)
+specific antigens lower the chance of adverse reactions
-difficult to develop

---conjugate (Haemophilus influanzae type b, stroptococcal pneumonia)
+primes infant immune systems to recognize certain bacteria
(-)


3ª geração (other)
---recombinant vector (Ebola, in clinical testing)
+mimics natural infection, resulting i strong immune response
-too early to tell

---DNA (HPV, Zika, both in clinical testing)
+strong humoral and cellular immune response, relatively inexpensive to manufacture
-not yet available
---RNA (SARS-Cov2, Zika and CMV in progress)

11

Vacinas com microrganismos vivos atenuados

• Microrganismos são atenuados de maneira a perderem a capacidade de
causar doença no hospedeiro.
-> Retêm a capacidade de crescimento no hospedeiro

• Bactérias são cultivadas por longos períodos de tempo em condições adversas; aquelas que sobrevivem não são capazes de se adaptar às
condições óptimas de crescimento no hospedeiro

• No caso dos vírus, estes podem ser cultivados em células de hospedeiros
não naturais, acumulando mutações que os podem enfraquecer.

• Exemplos de deste tipo de vacinas: vacina do sarampo, da papeira e da rubéola.

12

Imunização ativa -- Microrganismos vivos atenuados - pro e contras

Vantagens
< nº de inoculações
Induz respostas celulares
Não são necessários adjuvantes
< risco de hipersensibilidade
Mais barata

Desvantagens
Reversão para uma forma virulenta
Risco de contaminação com outros microrganismos
Elevado custo de produção e tempo de semi-vida curto.
Requer refrigeração (rede de frio: 20 a 80% do preço)

13

Vacinas com microrganismos mortos ou inativados

• Inativação de microrganismos pelo calor ou métodos químicos: Formaldeído (“cross-linking” de proteínas e ácidos nucleicos);
Acetona ou álcool (desnaturação);
Alquilação, óxido de etileno (cross-linking de ácidos nucleicos sem afetar as
proteínas de superfície)

--> Incapazes de replicação no hospedeiro
--> Epitopos têm que ser mantidos após o processo de inativação dos microrganismos

• Requer boosts frequentemente

• Riscos:
-> Microrganismo tem que ser crescido em larga escala antes da inativação, o que implica riscos para quem está diretamente envolvido no
processo de manufaturação

-> Inativação pode não ser 100% eficiente

• Exemplos: Vacina contra Bordetella pertussis, vacina contra febre tifóide, vacina da
gripe

14

Imunização ativa - Microrganismos inativados (mortos) - pros e contras

Vantagens
Estáveis no armazenamento
Mais seguras que vacinas vivas
Menor risco de provocar doença por virulência residual
Menor probabilidade de conter
microrganismos contaminantes

Desvantagens
Imunização menos potente
Imunizações repetidas
(aumento do custo)
Uso de adjuvantes pode levar a reações indesejáveis (ex.
hipersensibilidades)
Pode ser variável de lote para lote

15

Imunização ativa -
Macromoléculas purificadas

• Macromoléculas purificadas de microrganismos

• Toxoides
-> Algumas bactérias são patogénicas devido à produção de exotoxinas;
estas são purificadas, inativadas com formaldeído dando origem ao toxoide que é utilizado na imunização
-> O SI é então capaz de neutralizar a toxina aquando da infeção natural


Vantagens
Evitam alguns dos riscos presentes em vacinas com microrganismos atenuados ou inativados

Desvantagens
Necessário selecionar antigénios importantes
Selecionar modo de administração de antigénios de modo a estimular respostas imunes protetoras
Na ausência de adjuvantes alguns antigénios podem induzir tolerância

16

Vacinas conjugadas

Quando as vacinas de
subunidades são pouco
imunogénicas, estas podem ser acopoladas a estimuladores fortes
e.g. polissacárido de Haemophilus influenzae (não imunogénico) associado com toxoide tetânico que é
altamente imunogénico, resultando em imunidade ao Haemophilus!!

17

Mecanismos de ação dos adjuvantes

• Adjuvantes são substâncias
essenciais para aumentar e
direcionar a resposta
imunológica adquirida a Ag
vacinais!!

ver esquema? Ag-Adjuvant na vacina: 1. depot effect, apc recruitment
2. PRR activation
3. inflammassome activation
4. immune cell presentation, MHC presetation
--> opsonizing antibodies, neutralizing antibodies

18

Imunização ativa -
Vacinas de DNA - pros e contras

Vantagens
Proteínas expressas na sua forma natural no hospedeiro
Induzem resposta humoral e celular
Memória imunológica
Custo de produção reduzido
Eficazes sem necessitar de adjuvantes
Baixo risco, não necessitam de
refrigeração

Desvantagens
Apenas antigénios proteicos

19

Vacinas de DNA - funcionamento

Induzem imunidade humoral e celular!!

The injected gene is expressed in the injected
muscle cell and in nearby APCs. The peptides from the protein encoded by the DNA are expressed on the surface of both cell types after
processing as an endogenous antigen by the MHC class I pathway.

Cells that present the antigen in the context of class I MHC molecules stimulate development of cytotoxic T cells.

The protein encoded by the injected DNA is also expressed as a soluble, secreted protein, which is taken up, processed, and presented in the context of class II MHC molecules. This pathway stimulates B-cell
immunity and generates antibodies and B-cell
memory against the protein

ver esquema!!

diseases for which DNA vaccines have entered clinical trials: infectious diseases (HIV, influenza, malaria, hep B, SARS, ebola, HPV, dengue, HSV, measles, malaria) + cancer (Bcell lymphoma, prostate cancer, melanoma, breast cancer, ovarian cancer, cervical cancer, ...)

20

Imunização ativa -
Vacinas de Vetores Recombinantes

Vantagens
Mimetizam infeção natural resultando em fortes respostas imunes

Microrganismos recombinantes:
Introdução de genes que codificam para proteínas de diferentes microrganismos em bactérias (ex. BCG ou Salmonella, Shigella, Listeria) ou em vírus (ex. poxvirus, vaccinia).

21

Produção de vacina utilizando um vector recombinante de vaccinia

Production of vaccine, using a recombinant vaccinia vector. Left: The gene that encodes the desired antigen (orange) is inserted into a plasmid vector adjacent to a vaccinia promoter (pink) and flanked on either side by the vaccinia thymidine kinase (TK) gene (green). Right: When tissue culture cells are incubated simultaneously with
vaccinia virus and the recombinant plasmid, DNA encoding the antigen is inserted into the vaccinia virus genome by homologous recombination at the site of the nonessential TK gene, resulting in a TK recombinant virus. Cells
containing the recombinant vaccinia virus are selected by addition of bromodeoxyuridine (BrdU), which kills TK
cells.

22

Pipeline tradicional e acelerada para desenvolvimento de
uma vacina

Vaccine development for SARS-CoV-2 is following an accelerated timeline. Because of knowledge gained from the initial development of vaccines for SARS-CoV and MERS-CoV, the discovery phase was omitted.

Existing processes were adopted, and phase I/II trials were started. Phase III trials were initiated after the interim analysis of phase I/II results, with several clinical trial stages running in parallel.

In the meantime, vaccine producers have started the large-scale production of several vaccine candidates, at risk.

The exact pathway by which these vaccine candidates will be licensed—for example, through an initial emergency use authorization—is not yet clear.

=> 10 months to 1.5 years total

23

SARS-Cov2

• Proteína spike é o principal alvo de vacinas contra o SARS-Cov-2, uma vez que é capaz de induzir a produção de Ab neutralizantes

[Receptor-binding-domain of spike proteins binds to ACE2 receptor = Angiotensin-converting enzyme 2 R]

• Em Setembro 2020: 234 vacinas em desenvolvimento

24

Plataformas vacinais utilizadas no desenvolvimento de vacinas contra o SARS-CoV-2

attenuated virus
protein subunit (spike)
DNA containing spike sequence
RNA containing spike sequence
Replicating viral vector
Non-replicating viral vector
VLP

25

Vacinas contra o SARS-Cov-2 - comparação!

Moderna (US)
type: mRNA
Ag: full-length spike protein with proline substitutions
dose: 100 ug
dosage:2 doses 28d apart
storage conditions: -25 to -15ºC, 2-8ºC for 30d, room temperature < 12h
efficacy against severe COVID-19: 100% 14d after second dose
overall efficacy: 92.1% 14d after 1 dose, 94% 14d after second dose
current approvals: EUA - US, EU, Canada, UK


Pfizer-BioNTech (US)
type: mRNA
Ag: full-length spike protein with proline substitutions
dose: 30 ug
dosage: 2 doses 21d apart
storage conditions: -80 to -60ºC, 2-8ºC for 5d, room temperature < 2h
efficacy against severe COVID-19: 88.9% after 1 dose
overall efficacy: 52% after 1 dose, 94.6% after second dose
current approvals: EUA - US, EU, Canada, UK

Janssen/ Johnson&Johnsons (US)
type: viral vector
Ag: recombinant, replication-incompetent human adenovirus serotype 26 vector encoding a full-length, stabilized SARS-Cov-2 S protein
dose: 5*10^10 viral particles
dosage: 1 dose
storage conditions: -20ºC, 2-8ºC for 3 mo
efficacy against severe COVID-19: 85% after 28d, 100% after 49d
overall efficacy: 72% in the US, 66% in latin america (at 28d)
current approvals: EUA - US, EU, Canada

AstraZeneca/Oxford (UK)
type: viral vector
Ag: replication-deficient chimpanzee adenoviral vector with the SARS-Cov-2 S protein
dose:5*10^10 viral particles
dosage: 2 doses 28d apart
storage conditions: 2-8ºC for 6mo
efficacy against severe COVID-19: 100% 21d after first dose
overall efficacy: 64.1% after 1 dose, 70.4% 14d after second dose
current approvals: EUA - WHO/Covax, the UK, India, and Mexico

+outras...
Novavax (US) - protein subunit ... EUA application planned
CureVac/GSK (DE) - mRNA - ...
Sputnik V (RU) - viral vector -... EUA - Russia, Belarus, Argentina, Serbia, UAE, Algeria, Palestine, and Egypt
Sinovac (CH) - inactivated virus - ... EUA - China, Brazil, Columbia, Bolivia, Brazil, Chile, Uruguay, Turkey, Indonesia, Azerbaijan
Sinopharm (CH) - inactivated virus - ... EUA - China, UAE, Bahrain, Serbia, Peru, Zimbabwe

(EUA - emergency use application)

26

Vacinas contra SARS-Cov-2 - indução da imunidade

The two vaccine formulations —mRNA encoding the SARS-CoV-2 spike (S) protein encapsulated in lipid nanoparticles or adenovirus (AdV) vectors encoding the S protein — gain entry into dendritic cells (DCs) at the injection site or within lymph nodes, resulting in production of high levels of S protein. In addition, innate sensors are triggered by the intrinsic adjuvant activity of the vaccines, resulting in production of type I interferon and multiple pro-inflammatory cytokines and chemokines.

RNA sensors such as Toll-like receptor 7 (TLR7) and MDA5 are triggered by the mRNA vaccines, and TLR9 is the major double-stranded DNA sensor for the AdV vaccine.

The resultant activated DCs present antigen and co-stimulatory molecules to S protein-specific naive T cells, which become activated and differentiated into effector cells to form cytotoxic T lymphocytes or helper T cells. T follicular helper (TFH) cells help S protein-specific B cells to differentiate into antibodysecreting plasma cells and promote the production of high affinity anti-S protein antibodies.

Following vaccination, S protein-specific memory T cells and B cells develop and circulate along with high affinity SARS-CoV-2 antibodies, which
together help prevent subsequent infection with SARS-CoV-2.

27

Key concepts

• Vaccination is a powerful strategy for preventing infections. The most effective vaccines are those that stimulate the production of high-affinity antibodies and memory cells. Many approaches for vaccination are in clinical use and being tried for various infections.
• The development of a new vaccine requires much basic science research, huge investments of time and money in development (with more failures than successes), and a clear prior delineation of the specific immune targets of a vaccination program, called correlates of immune protection.
• Passive immunity, which is only temporary and does not engage the host’s immune response or generate memory, can be acquired naturally (e.g., in utero transplacental IgG) or delivered artificially to protect individuals from subsequent infectious disease or recent venom exposures, and in those
who lack humoral responses.
• Active immunity can be triggered by either natural infection or artificial exposure to some form of a pathogen, such as a vaccine, with a goal of inducing a memory response that will be protective in the future.
• The introduction of vaccine campaigns, especially in children, has vastly reduced the risk of death from infectious disease worldwide.

• Herd immunity occurs when a large portion of a community (the herd) becomes immune to a disease, making the spread of disease from person
to person unlikely. As a result, the whole community becomes protected — not just those who are immune. The more contagious a disease is, the
greater the proportion of the population that needs to be immune to the disease to stop its spread.
• Live attenuated vaccines are weakened forms of the infectious agent used to trigger a robust adaptive immune response. Advantages include effector cell types well matched with natural infection (including CTLs) and strong,
long-lived, protective memory after even a single exposure. An important disadvantage is the potential for reversion to more virulent forms that can cause disease.
• An infectious organism can be killed or chemically inactivated, and then administered as a means to trigger protective adaptive immune responses.
Advantages include the low risk of reversion and disease, plus rapid production times. Disadvantages include lower immunogenicity, poor cellmediated immune responses (especially CTLs), and a weaker protection
that can necessitate booster shots.
• Subunit vaccines use just a part of an inactivated or killed infectious agent; thus they share many of the same advantages and disadvantages, with the added advantage of simpler, safer, and more rapid production time.

• When subunit antigens are poor immune stimulators they can be combined with strong immune activators, either as a fused protein (conjugate) or in a mixture of proteins (multivalent), allowing the strong immunogen to act as a carrier for the weaker antigen, inducing a more robust immune response against both.
• Adjuvants are additives that can be mixed in with a vaccine to stimulate innate signals that help to instruct and enhance the adaptive response, and are modelled on natural PAMPs known to help direct specific
adaptive pathways.
• Viruses and other microbes that replicate inside cells but cause no disease can be used as live delivery vehicles for fragments of pathogens.
These recombinant vector vaccines retain many of the same advantages of live attenuated vaccines (cell-mediated responses, more robust immunity) and fewer of the disadvantages (low or nonexistent reversion
potential and moderate production times).
• DNA vaccines aim to deliver selected genetic material from an infectious agent into host cells as a means for host-based gene expression and immune activation.
• RNA vaccines work by introducing an mRNA sequence encoding for a
disease specific antigen. These vaccines are faster and cheaper to produce than traditional vaccines, and a RNA based vaccine is also safer
for the patient, as they are not produced using infectious elements.