9/27 Flashcards
Clinical Research vs. Trials
Clinical Research: research on humans in a clinical setting, many design types like descriptive, cohort, case-control, cross-sectional, etc.
Clinical Trials: randomized, gold standard for determining safety and effectiveness
Special Features of RCTs
Always prospective, at baseline all participants are unexposed and outcome-negative
Involve increased regulation and safety is evaluated by an external board
Participants and investigators don’t choose exposure groups, assigned randomly
Randomization minimizes confounding bias at baseline, has no effect on bias during followup, approximates the counterfactual
Simple vs. Blocked Randomization
Simple: like flip a coin, don’t know what assignment comes next
Blocked: simple randomization but within known block sizes
Permuted Blocked: size of the block is also randomly assigned
Blinding
Balances placebo effect, can do without placebo
Knowledge of group assignment can affect compliance and retention
Reduces differential assessment of outcomes (ascertainment bias), subjective outcomes like pain can have a lot of bias, more objective things like lab assay less likely to be biased even if unblinded
Double blind: includes patients, investigators, outcome assessors
Triple blind: same as double blind and also data analysts
RCT Phases
I: small number o healthy people like 10, closely monitor with focus on safety
II: small number of subjects with condition to be treated like 100-200, expanded focus on safety plus preliminary efficacy
III: expanded controlled/uncontrolled studies, lot of subjects with condition to be treated like 200-1000, primary focus on efficacy plus extended safety considerations
IV: further characterize safety of drug by tracking adverse events, explore new therapeutic indications, marketing
Analysis of RCTs
Intention-to-treat: primary analytic approach, analyzed according to exposure assignment rather than actual exposure
Not allow for adjustments to con founders or adherence, measured how well it worked with warts and all of real life
Per protocol: as-treated or secondary analysis, examines confounders and adherence
TLR Signaling on Virally Infected Epithelial Cells
TLR signaling activates interferon response factors (IRFs) that initiate production of INFalpha/beta and secrete them
IFNalpha/beta does autocrine/paracrine signaling, initiate pathways to degrade viral RNA and prevent viral protein synthesis
Also increases MHC Class I presentation, favors proteasome production to degrade viral proteins for presentation
Day 0 and 1 of Influenza Virus
Enters respiratory tract and infects epithelial cells, viral genome enters host nucleus
Recognize pathogens via TLR, Dendritic cells and macrophages engulf virus in tissues, present antigen after upregulating MHC II and B7 expression, make systemic cytokines
Virally infected epithelial cells make Type 1 interferons
Complement Pathway
Day 1: Neutrophils help, Dendritic cells migrate to lymph nodes
Natural Killer Cells
Lyse virally infected cells with lytic granules, cytotoxicity increased by INFalpha/beta
IL-12 and TNFalpha made by macrophages activate NK cells to make IFNgamma, creates positive feedback loop
NK cells peak at about 3-4 days
Inhibitory receptors bind self MHC 1 receptors so kill Cell if not have MHC 1 cuz downregulated by pathogen, compensatory mechanism since CD8+ T cells need MHC 1 to lyse
Kill stressed cells expressing MIC
Day 2 of Influenza
NK cells come to help
Lectin binding pathway of Complement
Fever
Days 3-7 of Virus
Day 3: dendritic cells present viral antigens to naive T cells
Day 4: T cells upregulate IL-2Ralpha and IL-2 to promote T cell proliferation
Day 5: cytokines in the microenvironment promote CD4 T cell proliferation
Day 6: T cells activate B cells and migrate to the site of infection, Cytotoxic T cells help
Day 7: B cells and plasma cells migrate to the site of infection, make antibodies, classical Complement pathway (start day 3 if have C-reactive protein), antibody dependent cell mediated cytotoxicity by NK cells and antibodies
Day 8-25 of Virus
8-12: viral infection is eliminated
12-15: inflammation subsides, CTLA-4 on T cell, IL-10 and TGFbeta, macrophages clean up dead cells
15-25: memory B and T cells develop,mainly IgG
Early Events of HIV Infection
Mucosal routes of infection, Langerhans cells are submucosal dendritic cells with CD4 receptors and co-receptors that can be infected, still travel to lymph node
Dendritic cells can bind HIV with DC-SIGN but not be infected, travel to lymph node, interface with CD4+ T cell to transfer virus
Within days: CD4+ T cells, dendritic cells, tissue macrophages, monocytes, and Langerhans cells get infected
3 Steps of HIV Infection and then activation
- gp120 binds to CD4
- gp120 gets conformational change to bind to a co-receptor
CCR5: macrophage tropic, more common for sexual transmission, polymorphism in Europeans
CXCR4: lymphotropic
Activation: remain dormant until T cell activated, HIV preferentially infects and replicates in activated CD4 cells, NFkB does viral transcription of LTR
Clinical Definition of AIDS
CD4+ T Cell Count less than 200
Infected by opportunistic pathogen that is usually not pathogenic
Mean of 10 years to AIDS, quicker if have higher viral set point during latency
Virus Spike for HIV
Earliest indicator of HIV infection
Acute mononucleosis-like symptoms, happens in 50% of patients
4-11 days after exposure
Decline due to killing by activated CD8+ T cells
CD4+ T cell Loss
Measures extent of HIV, should be about 1000 if normal
- Directly from HIV infection
- Ongoing immune activation with CD4 cell apoptosis
- Attack by HIV specific CD8+ T cells
- Low thymic output
Humoral Response
Seroconversion: A few weeks after infection and end of acute phase, make antigens for envelope and capsid proteins
Window: Early on when infected but no antibodies
Use ELISA test to find antibodies, some false positives so need Western blot as confirmation test
Antibodies generated to HIV do not neutralize virus, antibodies select for mutated forms and overcome antibodies
Cellular Immune Response to HIV
Initial response to HIV includes large rise in HIV specific cytotoxic T cells, a broader cytotoxic T cell response results in a lower set point and better prognosis
CD8+ cells: directly kill cells and block HIV, broader response results in lower viral set point, function dependent on CD4+ cells
CD4+ cells: HIV specific CD4+ cells are generated during acute infection, activated CD4+ cells are preferentially infected by HIV, loss of CD4+ cells specific for HIV target is distinct to HIV
Lack of HIV specific CD4+ cells lead to inadequate maintenance of HIV specific CD8+ cytotoxic T cells that leave the host incapable of killing new HIV variants
HIV Treatment
Broadly neutralizing monoclonal antibodies can neutralize HIV, bind to conserved sites on gp120 and work for many different viral strains
Highly active antiretroviral therapy (HAART): drug cocktail, decreases plasma HIV RNA and make low level of ongoing replication
HIV in plasma falls and CD4 rise, little HIV antigen available to stimulate new CD4+ T cells made from thymus so no HIV specific CD4+ cells
CD8+ cells fall from their elevated levels
CD4+ count slowly rises, gradual lessening of immunosuppression and reduces susceptibility to infections
Replication-competent HIV remains latent in CD4 cells and will respond to high levels if antiretroviral therapy is stopped
Acute HIV infection symptoms
Fever, swollen lymph glands, sweats, and sore throat
