(1) As can be seen from the figure, dendritic cells are ultimately derived from pluripotent hematopoietic stem cells; From the molecular level analysis, the mRNA molecules in various cells in the figure make protein molecules different, thus forming different kinds of cells; The function of phagocytes in specific immunity is to process antigens and present them to cells.

(2) Dendritic cells can activate T lymphocytes of the same species and make them proliferate and differentiate into effector T cells and memory cells, which belongs to cellular immunity.

(3) The researchers conducted the following experiments, please complete the relevant contents:

② Experimental grouping: The experimental design should conform to the control principle and univariate principle, so the treatment method of the control group is to inject the same amount of normal saline+cells into the tumor regularly.

③ Data collection and processing: The tumor volume of nude mice was measured regularly, averaged and plotted as a curve (Figure 2).

④ Result analysis: According to Figure 2, it can be seen that the tumor in the control group is the largest, the tumor in the treatment group is smaller, and the tumor in the intensive treatment group is the smallest, so it can be concluded that: a. Dendritic cells can induce cells to produce anti-tumor immune response;

B. With the increase of cell dose, the ability of dendritic cells to induce anti-tumor immune response is enhanced.

This experiment can not rule out whether dendritic cells have anti-tumor immune response, so the control group should be supplemented: a certain amount of dendritic cells should be injected into the tumor regularly.

So the answer is:

(1) mRNA molecules (or mRNA and protein molecules) of pluripotent hematopoietic stem cells? Processing antigens and presenting them to cells (or swallowing and digesting antigen-antibody complexes)

(2) effector T cells? Cellular immunity (or specific immunity) of memory cells

(3) Equal amount of normal saline+cells

A. Dendritic cells can induce anti-tumor immune response.

B. With the increase of cell dose, the ability of dendritic cells to induce anti-tumor immune response is enhanced.

Supplementary control group: inject a certain amount of dendritic cells into the tumor regularly.