Corticosteroids (such as prednisone or dexamethasone ) are referred to as "transitional" medicines for the treatment of cluster headaches , because they are sometimes used to break a cycle of cluster headaches. They are paired with medicines that stop (abortive) or prevent (prophylactic) additional headaches during a headache cycle. Often, within 2 to 4 days after starting treatment with corticosteroids, you will become headache-free. By the time the corticosteroids are stopped—their use is often tapered within 6 to 8 weeks of starting and then discontinued—the medicines used to prevent cluster headaches, such as verapamil , have taken effect.
A vaccine that targets PCSK9 has been developed to treat high LDL-particle concentrations. The vaccine uses a VLP ( virus-like particle ) as an immunogenic carrier of an antigenic PCSK9 peptide. VLP's are viruses that have had their DNA removed so that they retain their external structure for antigen display but are unable to replicate; they can induce an immune response without causing infection. Mice and macaques vaccinated with bacteriophage VLPs displaying PCSK9-derived peptides developed high-titer IgG antibodies that bound to circulating PCSK9. Vaccination was associated with significant reductions in total cholesterol, free cholesterol, phospholipids, and triglycerides. 
So CD4 counts appear to be a useful tool in assessing risk, but other factors also contribute such as lung architecture. In a retrospective study of 74 patients with interstitial lung disease on corticosteroids, 7 patients developed PCP. The mean dose at time of diagnosis was prednisone 37mg with mean duration of 10 weeks. CD4 counts ranged from 59 to 836, with a mean of 370 . The authors argued that due to their underlying lung disease, the patients were at higher risk for PCP and became infected at higher CD4 counts than patients with other underlying diseases.