Tumour Necrosis Factor blocker or TNF blocker refers to a drug that blocks TNF, which is a protein made by your own body as part of your natural immune system, in response to inflammation. By injecting a TNF Blocker you can reduce the inflammation by supressing the immune system.
The drugs have reported great results for those not bale to control the pain with NSAIDs for example, but the down side appears to be an increase risk of infection due to a low immune system. Patients on these drugs according to Wikipedia are often advised to limit their exposure to others who may be carrying a virus like a cough or cold and to suspend treatment if you do catch something.