肺炎球菌是引起肺炎、菌血症、儿童中耳炎和细菌性脑膜炎的主要原因。现在使用的肺炎球菌多糖疫苗为胸腺非依赖性疫苗 ,对老人和 2岁以下的幼儿无保护作用。虽然最近批准的结合疫苗能诱导 T细胞依赖性免疫 ,但是它的作用也有限 ,在某些人群中仍缺乏应答。因此研制胸腺依赖性肺 Pneumococcus is the main cause of pneumonia, bacteremia, otitis media in children and bacterial meningitis. The pneumococcal polysaccharide vaccine now being used is a thymus-independent vaccine that has no protective effect on the elderly and children under 2 years of age. Although the recently approved combination vaccine induces T cell-dependent immunity, its role is limited and in some populations there is still a lack of response. Therefore, the development of thymus-dependent lungs